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  • 1.
    Abramowicz, Konrad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Häger, Charlotte
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering, Sjukgymnastik.
    Hérbert-Losier, Kim
    Swedish Winter Sports Research Centre Mid Sweden; University Department of Health Sciences, Östersund, Sweden.
    Pini, Alessia
    MOX – Department of Mathematics, Politecnico di Milano.
    Schelin, Lina
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering, Fysioterapi.
    Strandberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Vantini, Simone
    MOX – Department of Mathematics, Politecnico di Milano.
    An inferential framework for domain selection in functional anova2014Ingår i: Contributions in infinite-dimensional statistics and related topics / [ed] Bongiorno, E.G., Salinelli, E., Goia, A., Vieu, P, Esculapio , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a procedure for performing an ANOVA test on functional data, including pairwise group comparisons. in a Scheff´e-like perspective. The test is based on the Interval Testing Procedure, and it selects intervals where the groups significantly differ. The procedure is applied on the 3D kinematic motion of the knee joint collected during a functional task (one leg hop) performed by three groups of individuals.

  • 2.
    Abramowicz, Konrad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Häger, Charlotte
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering, Fysioterapi.
    Pini, Alessia
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Statistical Sciences, Università Cattolica del Sacro Cuore, Milan, Italy.
    Schelin, Lina
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Sjöstedt de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Vantini, Simone
    Nonparametric inference for functional-on-scalar linear models applied to knee kinematic hop data after injury of the anterior cruciate ligament2018Ingår i: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 45, nr 4, s. 1036-1061Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Motivated by the analysis of the dependence of knee movement patterns during functional tasks on subject-specific covariates, we introduce a distribution-free procedure for testing a functional-on-scalar linear model with fixed effects. The procedure does not only test the global hypothesis on the entire domain but also selects the intervals where statistically significant effects are detected. We prove that the proposed tests are provided with an asymptotic control of the intervalwise error rate, that is, the probability of falsely rejecting any interval of true null hypotheses. The procedure is applied to one-leg hop data from a study on anterior cruciate ligament injury. We compare knee kinematics of three groups of individuals (two injured groups with different treatments and one group of healthy controls), taking individual-specific covariates into account.

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  • 3.
    Abramowicz, Konrad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Pini, Alessia
    Department of Statistical Sciences, Università Cattolica del Sacro Cuore, Milan, Italy.
    Schelin, Lina
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Sjöstedt de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Stamm, Aymeric
    Department of Mathematics Jean Leray, UMR CNRS 6629, Nantes University, Nantes, France.
    Vantini, Simone
    MOX – Modelling and Scientific Computing Laboratory, Department of Mathematics, Politecnico di Milano, Milan, Italy.
    Domain selection and family-wise error rate for functional data: a unified framework2023Ingår i: Biometrics, ISSN 0006-341X, E-ISSN 1541-0420, Vol. 79, nr 2, s. 1119-1132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Functional data are smooth, often continuous, random curves, which can be seen as an extreme case of multivariate data with infinite dimensionality. Just as component-wise inference for multivariate data naturally performs feature selection, subset-wise inference for functional data performs domain selection. In this paper, we present a unified testing framework for domain selection on populations of functional data. In detail, p-values of hypothesis tests performed on point-wise evaluations of functional data are suitably adjusted for providing a control of the family-wise error rate (FWER) over a family of subsets of the domain. We show that several state-of-the-art domain selection methods fit within this framework and differ from each other by the choice of the family over which the control of the FWER is provided. In the existing literature, these families are always defined a priori. In this work, we also propose a novel approach, coined threshold-wise testing, in which the family of subsets is instead built in a data-driven fashion. The method seamlessly generalizes to multidimensional domains in contrast to methods based on a-priori defined families. We provide theoretical results with respect to consistency and control of the FWER for the methods within the unified framework. We illustrate the performance of the methods within the unified framework on simulated and real data examples, and compare their performance with other existing methods.

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  • 4.
    Abramowicz, Konrad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Schelin, Lina
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Sjöstedt de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Strandberg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Multiresolution clustering of dependent functional data with application to climate reconstruction2019Ingår i: Stat, E-ISSN 2049-1573, Vol. 8, nr 1, artikel-id e240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a new nonparametric clustering method for dependent functional data, the double clustering bagging Voronoi method. It consists of two levels of clustering. Given a spatial lattice of points, a function is observed at each grid point. In the first‐level clustering, features of the functional data are clustered. The second‐level clustering takes dependence into account, by grouping local representatives, built from the resulting first‐level clusters, using a bagging Voronoi strategy. Depending on the distance measure used, features of the functions may be included in the second‐step clustering, making the method flexible and general. Combined with the clustering method, a multiresolution approach is proposed that searches for stable clusters at different spatial scales, aiming to capture latent structures. This provides a powerful and computationally efficient tool to cluster dependent functional data at different spatial scales, here illustrated by a simulation study. The introduced methodology is applied to varved lake sediment data, aiming to reconstruct winter climate regimes in northern Sweden at different time resolutions over the past 6,000 years.

  • 5.
    Abramowicz, Konrad
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Sjöstedt de Luna, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Strandberg, Johan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Nonparametric bagging clustering methods to identify latent structures from a sequence of dependent categorical data2022Ingår i: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 177, artikel-id 107583Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonparametric bagging clustering methods are studied and compared to identify latent structures from a sequence of dependent categorical data observed along a one-dimensional (discrete) time domain. The frequency of the observed categories is assumed to be generated by a (slowly varying) latent signal, according to latent state-specific probability distributions. The bagging clustering methods use random tessellations (partitions) of the time domain and clustering of the category frequencies of the observed data in the tessellation cells to recover the latent signal, within a bagging framework. New and existing ways of generating the tessellations and clustering are discussed and combined into different bagging clustering methods. Edge tessellations and adaptive tessellations are the new proposed ways of forming partitions. Composite methods are also introduced, that are using (automated) decision rules based on entropy measures to choose among the proposed bagging clustering methods. The performance of all the methods is compared in a simulation study. From the simulation study it can be concluded that local and global entropy measures are powerful tools in improving the recovery of the latent signal, both via the adaptive tessellation strategies (local entropy) and in designing composite methods (global entropy). The composite methods are robust and overall improve performance, in particular the composite method using adaptive (edge) tessellations.

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  • 6.
    Abramsson, Evelina
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Grind, Kajsa
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Skattning av kausala effekter med matchat fall-kontroll data2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
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  • 7.
    Abzhandadze, Tamar
    et al.
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Department of Occupational Therapy and Physiotherapy, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Lundström, Erik
    Department of Neuroscience, Neurology, Uppsala University, Akademiska Sjukhuset, Uppsala, Sweden.
    Buvarp, Dongni
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Eriksson, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Quinn, Terence J
    Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom.
    S Sunnerhagen, Katharina
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Neurocare, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Development of a short-form Swedish version of the Montreal Cognitive Assessment (s-MoCA-SWE): Protocol for a cross-sectional study2021Ingår i: BMJ Open, E-ISSN 2044-6055, Vol. 11, nr 5, artikel-id e049035Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Introduction: Short forms of the Montreal Cognitive Assessment (MoCA) have allowed quick cognitive screening. However, none of the available short forms has been created or validated in a Swedish sample of patients with stroke.

    The aim is to develop a short-form Swedish version of the MoCA (s-MoCA-SWE) in a sample of patients with acute and subacute stroke. The specific objectives are: (1) to identify a subgroup of MoCA items that have the potential to form the s-MoCA-SWE; (2) to determine the optimal cut-off value of s-MoCA-SWE for predicting cognitive impairment and (3) and to compare the psychometric properties of s-MoCA-SWE with those of previously developed MoCA short forms.

    Methods and analysis: This is a statistical analysis protocol for a cross-sectional study. The study sample will comprise patients from Väststroke, a local stroke registry from Gothenburg, Sweden and Efficacy oF Fluoxetine - a randomisEd Controlled Trial in Stroke (EFFECTS), a randomised controlled trial in Sweden. The s-MoCA-SWE will be developed by using exploratory factor analysis and the boosted regression tree algorithm. The cut-off value of s-MoCA-SWE for impaired cognition will be determined based on binary logistic regression analysis. The psychometric properties of s-MoCA-SWE will be compared with those of other MoCA short forms by using cross-tabulation and area under the receiving operating characteristic curve analyses.

    Ethics and dissemination: The Väststroke study has received ethical approval from the Regional Ethical Review Board in Gothenburg (346-16) and the Swedish Ethical Review Authority (amendment 2019-04299). The handling of data generated within the framework of quality registers does not require written informed consent from patients. The EFFECTS study has received ethical approval from the Stockholm Ethics Committee (2013/1265-31/2 on 30 September 2013). All participants provided written consent. Results will be published in an international, peer-reviewed journal, presented at conferences and communicated to clinical practitioners in local meetings and seminars.

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  • 8.
    Abzhandadze, Tamar
    et al.
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Department of Occupational Therapy and Physiotherapy, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Lundström, Erik
    Department of Medical Sciences, Neurology, Akademiska Sjukhuset, Uppsala, Sweden.
    Buvarp, Dongni
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Eriksson, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Quinn, Terence J.
    Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.
    Sunnerhagen, Katharina S.
    Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Neurocare, Rehabilitation Medicine, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Development of a Swedish short version of the montreal cognitive assessment for cognitive screening in patients with stroke2023Ingår i: Journal of Rehabilitation Medicine, ISSN 1650-1977, E-ISSN 1651-2081, Vol. 55, artikel-id jrm4442Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    OBJECTIVE: The primary objective was to develop a Swedish short version of the Montreal Cognitive Assessment (s-MoCA-SWE) for use  with patients with stroke. Secondary objectives were to identify an optimal cut-off value for the s-MoCA-SWE to screen for cognitive impairment and to compare its sensitivity with that of previously developed short forms of the Montreal Cognitive Assessment.

    DESIGN: Cross-sectional study.

    SUBJECTS/PATIENTS: Patients admitted to stroke and rehabilitation units in hospitals across Sweden.

    METHODS: Cognition was screened using the Montreal Cognitive Assessment. Working versions of the s-MoCA-SWE were developed using supervised and unsupervised algorithms.

    RESULTS: Data from 3,276 patients were analysed (40% female, mean age 71.5 years, 56% minor stroke at admission). The suggested s-MoCA-SWE comprised delayed recall, visuospatial/executive function, serial 7, fluency, and abstraction. The aggregated scores ranged from 0 to 16. A threshold for impaired cognition ≤ 12 had a sensitivity of 97.41 (95% confidence interval, 96.64-98.03) and positive predictive value of 90.30 (95% confidence interval 89.23-91.27). The s-MoCA-SWE had a higher absolute sensitivity than that of other short forms.

    CONCLUSION: The s-MoCA-SWE (threshold ≤ 12) can detect post-stroke cognitive issues. The high sensitivity makes it a potentially useful "rule-out" tool that may eliminate severe cognitive impairment in people with stoke.

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  • 9. Abzhandadze, Tamar
    et al.
    Reinholdsson, Malin
    Palstam, Annie
    Eriksson, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Sunnerhagen, Katharina S.
    Transforming self-reported outcomes from a stroke register to the modified Rankin Scale: a cross-sectional, explorative study2020Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 10, nr 1, artikel-id 17215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim was to create an algorithm to transform self-reported outcomes from a stroke register to the modified Rankin Scale (mRS). Two stroke registers were used: the Väststroke, a local register in Gothenburg, Sweden, and the Riksstroke, a Swedish national register. The reference variable, mRS (from Väststroke), was mapped with seven self-reported questions from Riksstroke. The transformation algorithm was created as a result of manual mapping performed by healthcare professionals. A supervised machine learning method—decision tree—was used to further evaluate the transformation algorithm. Of 1145 patients, 54% were male, the mean age was 71 y. The mRS grades 0, 1 and 2 could not be distinguished as a result of manual mapping or by using the decision tree analysis. Thus, these grades were merged. With manual mapping, 78% of the patients were correctly classified, and the level of agreement was almost perfect, weighted Kappa (Kw) was 0.81. With the decision tree, 80% of the patients were correctly classified, and substantial agreement was achieved, Kw = 0.67. The self-reported outcomes from a stroke register can be transformed to the mRS. A mRS algorithm based on manual mapping might be useful for researchers using self-reported questionnaire data.

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  • 10. Albano, Anthony D.
    et al.
    Wiberg, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Linking With External Covariates: Examining Accuracy by Anchor Type, Test Length, Ability Difference, and Sample Size2019Ingår i: Applied psychological measurement, ISSN 0146-6216, E-ISSN 1552-3497, Vol. 43, nr 8, s. 597-610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Research has recently demonstrated the use of multiple anchor tests and external covariates to supplement or substitute for common anchor items when linking and equating with nonequivalent groups. This study examines the conditions under which external covariates improve linking and equating accuracy, with internal and external anchor tests of varying lengths and groups of differing abilities. Pseudo forms of a state science test were equated within a resampling study where sample size ranged from 1,000 to 10,000 examinees and anchor tests ranged in length from eight to 20 items, with reading and math scores included as covariates. Frequency estimation linking with an anchor test and external covariate was found to produce the most accurate results under the majority of conditions studied. Practical applications of linking with anchor tests and covariates are discussed.

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  • 11.
    Ali, Hazrat
    et al.
    College of Science and Engineering, Hamad Bin Khalifa University, Doha, Qatar.
    Shah, Zubair
    College of Science and Engineering, Hamad Bin Khalifa University, Doha, Qatar.
    Alam, Tanvir
    College of Science and Engineering, Hamad Bin Khalifa University, Doha, Qatar.
    Wijayatunga, Priyantha
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Elyan, Eyad
    School of Computing Science and Digital Media, Robert Gordon University, Aberdeen, United Kingdom.
    Editorial: recent advances in multimodal artificial intelligence for disease diagnosis, prognosis, and prevention2024Ingår i: Frontiers in Radiology, ISSN 2673-8740, Vol. 3, artikel-id 1349830Artikel i tidskrift (Övrigt vetenskapligt)
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  • 12.
    Alshalabi, Mohamad
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Measures of statistical dependence for feature selection: Computational study2022Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The importance of feature selection for statistical and machine learning models derives from their explainability and the ability to explore new relationships, leading to new discoveries. Straightforward feature selection methods measure the dependencies between the potential features and the response variable. This thesis tries to study the selection of features according to a maximal statistical dependency criterion based ongeneralized Pearson’s correlation coefficients, e.g., Wijayatunga’s coefficient. I present a framework for feature selection based on these coefficients for high dimensional feature variables. The results are compared to the ones obtained by applying an elastic net regression (for high-dimensional data). The generalized Pearson’s correlation coefficient is a metric-based measure where the metric is Hellinger distance. The metric is considered as the distance between probability distributions. The Wijayatunga’s coefficient is originally proposed for the discrete case; here, we generalize it for continuous variables by discretization and kernelization. It is interesting to see how discretization work as we discretize the bins finer. The study employs both synthetic and real-world data to illustrate the validity and power of this feature selection process. Moreover, a new method of normalization for mutual information is included. The results show that both measures have considerable potential in detecting associations. The feature selection experiment shows that elastic net regression is superior to our proposed method; nevertheless, more investigation could be done regarding this subject.

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  • 13.
    Andersson, Björn
    et al.
    Uppsala universitet.
    Bränberg, Kenny
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Wiberg, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    kequate: The kernel method of test equating. R package version 1.1.02012Övrigt (Övrigt vetenskapligt)
    Abstract [en]

    Implements the kernel method of test equating using the CB, EG, SG, NEAT CE/PSE and NEC designs, supporting gaussian,logistic and uniform kernels and unsmoothed and pre-smoothed input data.

  • 14.
    Andersson, Björn
    et al.
    Uppsala universitet.
    Bränberg, Kenny
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Wiberg, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Performing the Kernel Method of Test Equating with the Package kequate2013Ingår i: Journal of Statistical Software, E-ISSN 1548-7660, Vol. 55, nr 6, s. 1-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In standardized testing it is important to equate tests in order to ensure that the test takers, regardless of the test version given, obtain a fair test. Recently, the kernel method of test equating, which is a conjoint framework of test equating, has gained popularity. The kernel method of test equating includes five steps: (1) pre-smoothing, (2) estimation of the score probabilities, (3) continuization, (4) equating, and (5) computing the standard error of equating and the standard error of equating difference. Here, an implementation has been made for six different equating designs: equivalent groups, single group, counter balanced, non-equivalent groups with anchor test using either chain equating or post- stratification equating, and non-equivalent groups using covariates. An R package for the kernel method of test equating called kequate is presented. Included in the package are also diagnostic tools aiding in the search for a proper log-linear model in the pre-smoothing step for use in conjunction with the R function glm.

  • 15.
    Andersson, Björn
    et al.
    Statistiska institutionen, Uppsala universitet.
    Waernbaum, Ingeborg
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Sensitivity analysis of violations of the faithfulness assumption2014Ingår i: Journal of Statistical Computation and Simulation, ISSN 0094-9655, E-ISSN 1563-5163, Vol. 84, nr 7, s. 1608-1620Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    We study implications of violations of the fatihfulness condition due to parameter cancellations on estimation of the DAG skeleton. Three settings are investigated: when i) faithfulness is guaranteed ii) faithfulness is not guaranteed and iii) the parameter distributions are concentrated around unfaithfulness (near-unfaithfulness). In a simulation study the effetcs of the different settings are compared using the PC and MMPC algorithms. The results show that the performance in the faithful case is almost unchanged compared to the unrestricted case whereas there is a general decrease in performance under the near-unfaithful case as compared to the unrestricted case. The response to near-unfaithful parameterisations is similar between two algorithms, with the MMPC algorithm having higher true positive rates and the PC algorithm having lower false positive rates.

  • 16.
    Andersson, Björn
    et al.
    Beijing Normal University.
    Wiberg, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Item response theory observed-score kernel equating2017Ingår i: Psychometrika, ISSN 0033-3123, E-ISSN 1860-0980, Vol. 82, nr 1, s. 48-66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Item response theory (IRT) observed-score kernel equating is introduced for the non-equivalent groups with anchor test equating design using either chain equating or post-stratification equating. The equating function is treated in a multivariate setting and the asymptotic covariance matrices of IRT observed-score kernel equating functions are derived. Equating is conducted using the two-parameter and three-parameter logistic models with simulated data and data from a standardized achievement test. The results show that IRT observed-score kernel equating offers small standard errors and low equating bias under most settings considered.

  • 17. Andersson, Carolyn J.
    et al.
    Embretson, Susan
    Meulman, Jacqueline
    Moustaki, Irini
    von Davier, Alina A.
    Wiberg, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Yan, Duanli
    Stories of successful careers in psychometrics and what we can learn from them2020Ingår i: Quantitative psychology: 84th annual meeting of the Psychometric Society, Santiago, Chile, 2019 / [ed] Marie Wiberg, Dylan Molenaar, Jorge González, Ulf Böckenholt, and Jee-Seon Kim, New York: Springer, 2020, s. 1-17Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This paper was inspired by the presentations and discussions from the panel "Successful Careers in Academia and Industry and What We Can Learn from Them”" that took place at the IMPS meeting in 2019. In this paper, we discuss what makes a career successful in academia and industry and we provide examples from the past to the present. We include education and career paths as well as highlights of achievements as researchers and teachers. The paper provides a brief historical context for the representation of women in psychometrics and an insight into strategies for success for publishing, for grant applications and promotion. The authors outline the importance of interdisciplinary work, the inclusive citation approaches, and visibility of research in academia and industry. The personal stories provide a platform for considering the needs for a supportive work environment for women and for work-life balance. The outcome of these discussions and reflections of the panel members are included in the paper.

  • 18.
    Andersson, Magnus N.
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Sund, Malin
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Svensson, Johan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Björkgren, Annika
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Onkologi.
    Wiberg, Rebecca
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB), Anatomi. Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Handkirurgi.
    Prophylactic mastectomy – Correlation between skin flap thickness and residual glandular tissue evaluated postoperatively by imaging2022Ingår i: Journal of Plastic, Reconstructive & Aesthetic Surgery, ISSN 1748-6815, E-ISSN 1878-0539, Vol. 75, nr 6, s. 1813-1819Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Women with an increased hereditary risk of breast cancer can undergo risk-reducing prophylactic mastectomy. However, there is a balance between how much subcutaneous tissue should be resected to achieve maximal reduction of glandular tissue, while leaving viable skin flaps.

    Methods: Forty-five women previously operated with prophylactic mastectomy underwent magnetic resonance tomography (MRT) and ultrasound (US) to investigate the correlation between skin flap thickness and residual glandular tissue. Residual glandular tissue was documented as being present or not present, but not quantified, as the amount of residual glandular tissue in many cases was considered too small to make reliable volume quantifications with available tools. Since a mastectomy skin flap thickness of 5 mm is discussed as an oncologically safe thickness in the literature, this was used as a cut-off.

    Results: Following prophylactic mastectomy, residual glandular tissue was detected in 39.3% of all breasts and 27.9% of all the breast quadrants examined by MRT, and 44.1% of all breasts and 21.7% of all the breast quadrants examined by US. Residual glandular tissue was detected in 6.9% of the quadrants in skin flaps ≤ 5 mm and in 37.5% of the quadrants in skin flaps > 5 mm (OR 3.07; CI = 1.41–6.67; p = 0.005). Furthermore, residual glandular tissue increased significantly already when the skin flap thickness exceeded 7 mm.

    Conclusions: This study highlights that complete removal of glandular breast tissue during a mastectomy is difficult and suggests that this is an unattainable goal. We demonstrate that residual glandular tissue is significantly higher in skin flaps > 5 mm in comparison to skin flaps ≤ 5 mm, and that residual glandular tissue increases significantly already when the flap thickness exceeds 7 mm.

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  • 19.
    Andersson, Sara
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå University Hospital.
    Josefsson, Maria
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Umeå universitet, Samhällsvetenskapliga fakulteten, Enheten för demografi och åldrandeforskning (CEDAR).
    Stiernman, Lars J.
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Rieckmann, Anna
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi. Center for the Economics of Aging, Max Planck Institute for Social Law and Social Policy, Germany.
    Cognitive decline in Parkinson’s disease: a subgroup of extreme decliners revealed by a data-driven analysis of longitudinal progression2021Ingår i: Frontiers in Psychology, E-ISSN 1664-1078, Vol. 12, artikel-id 729755Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cognitive impairment is an important symptom of Parkinson’s disease (PD) and predicting future cognitive decline is crucial for clinical practice. Here, we aim to identify latent sub-groups of longitudinal trajectories of cognitive change in PD patients, and explore predictors of differences in cognitive change. Longitudinal cognitive performance data from 349 newly diagnosed PD patients and 145 healthy controls from the Parkinson Progression Marker Initiative were modeled using a multivariate latent class linear mixed model. Resultant latent classes were compared on a number of baseline demographics, and clinical variables, as well as cerebrospinal fluid (CSF) biomarkers and striatal dopamine transporter (DAT) density markers of neuropathology. Trajectories of cognitive change in PD were best described by two latent classes. A large subgroup (90%), which showed a subtle impairment in cognitive performance compared to controls but remained stable over the course of the study, and a small subgroup (10%) which rapidly declined in all cognitive performance measures. Rapid decliners did not differ significantly from the larger group in terms of disease duration, severity or motor symptoms at baseline. However, rapid decliners had lower CSF amyloidß42 levels, a higher prevalence of sleep disorder and pronounced loss of caudate DAT density at baseline. These data suggest the existence of a distinct minority sub-type of PD in which rapid cognitive change in PD can occur uncoupled from motor symptoms or disease severity, likely reflecting early pathological change that extends from motor areas of the striatum into associative compartments and cortex.

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  • 20.
    Andersson Tano, Ingrid
    et al.
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Vännman, Kerstin
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    A multivariate process capability index based on the first principal component only2013Ingår i: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 29, nr 7, s. 987-1003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Often the quality of a process is determined by several correlated univariate variables. In such cases, the considered quality characteristic should be treated as a vector. Several different multivariate process capability indices (MPCIs) have been developed for such a situation, but confidence intervals or tests have been derived for only a handful of these. In practice, the conclusion about process capability needs to be drawn from a random sample, making confidence intervals or tests for the MPCIs important. Principal component analysis (PCA) is a well-known tool to use in multivariate situations. We present, under the assumption of multivariate normality, a new MPCI by applying PCA to a set of suitably transformed variables. We also propose a decision procedure, based on a test of this new index, to be used to decide whether a process can be claimed capable or not at a stated significance level. This new MPCI and its accompanying decision procedure avoid drawbacks found for previously published MPCIs with confidence intervals. By transforming the original variables, we need to consider the first principal component only. Hence, a multivariate situation can be converted into a familiar univariate process capability index. Furthermore, the proposed new MPCI has the property that if the index exceeds a given threshold value the probability of non-conformance is bounded by a known value. Properties, like significance level and power, of the proposed decision procedure is evaluated through a simulation study in the two-dimensional case. A comparative simulation study between our new MPCI and an MPCI previously suggested in the literature is also performed. These studies show that our proposed MPCI with accompanying decision procedure has desirable properties and is worth to study further.

  • 21.
    Andersson Tano, Ingrid
    et al.
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Vännman, Kerstin
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Comparing confidence intervals for multivariate process capability indices2012Ingår i: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 28, nr 4, s. 481-495Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multivariate process capability indices (MPCIs) are needed for process capability analysis when the quality of a process is determined by several univariate quality characteristics that are correlated. There are several different MPCIs described in the literature, but confidence intervals have been derived for only a handful of these. In practice, the conclusion about process capability must be drawn from a random sample. Hence, confidence intervals or tests for MPCIs are important. With a case study as a start and under the assumption of multivariate normality, we review and compare four different available methods for calculating confidence intervals of MPCIs that generalize the univariate index Cp. Two of the methods are based on the ratio of a tolerance region to a process region, and two are based on the principal component analysis. For two of the methods, we derive approximate confidence intervals, which are easy to calculate and can be used for moderate sample sizes. We discuss issues that need to be solved before the studied methods can be applied more generally in practice. For instance, three of the methods have approximate confidence levels only, but no investigation has been carried out on how good these approximations are. Furthermore, we highlight the problem with the correspondence between the index value and the probability of nonconformance. We also elucidate a major drawback with the existing MPCIs on the basis of the principal component analysis. Our investigation shows the need for more research to obtain an MPCI with confidence interval such that conclusions about the process capability can be drawn at a known confidence level and that a stated value of the MPCI limits the probability of nonconformance in a known way.

  • 22.
    Andersson, Tobias
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Golovlev, Jegor
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Prediktion av bruttoregionalprodukt: Prognosmodellering som förkortar tiden mellan officiella siffror och prognos2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Arbetet har utforskat möjligheten och precisionen av BRP-prediktion för tre statistiska metoder; linjär regression, regressionsträd och modellträd. För modellutvärdering har testfelsskattning erhållen genom korsvalidering och en jämförelse mot Statistiska Centralbyråns (SCB) prognos av BRP används. Resultatet visar att regressionsträd inte lämpar sig för BRP-prediktion, medan de andra två lyckas med rimlig felmarginal. Procentuell avvikelse för metoden som ligger närmast SCB:s prognos har 0,3 i genomsnitt och standardavvikelse 3,0.

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  • 23.
    Andersson, Tore
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Borgström, Jonas
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Analys av bortfallets påverkan i Riksstrokes kvalitetsregister2020Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Akut stroke är en allvarlig och livshotande sjukdom som ofta leder till fysiska och kognitiva funktionsnedsättningar. Riksstroke är ett kvalitetregister som samlar in och tillhandahåller information om strokevården i Sverige. Under 2019–2020 pågår ett omfattande valideringsarbete där analys av bortfallet inom registret utförs. Syftet med uppsatsen var att som i en del av detta arbete analysera omfattningen av bortfallet i flera faktorer och om det fanns en skillnad mellan grupperna kön, ålder och sjukhus. Därefter testades två metoder för bortfallshantering, complete case analysis och multipel imputations by chained equation (MICE). Dessa utvärderades genom att jämföra de skattade oddskvoterna för död inom 90 dagar efter inskrivning på sjukhus. Resultatet visade att det fanns stora skillnader i bortfall mellan män och kvinnor, åldersgrupper och sjukhusen. Där kan en stor del av skillnaden i bortfall troligtvis kan förklaras av åldern på patienterna. Det två utvärderade metoderna producerade jämförbara resultat.

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  • 24.
    Andersson-Evelönn, Emma
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Vidman, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Källberg, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Landfors, Mattias
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Liu, Xijia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Ljungberg, Börje
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Hultdin, Magnus
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Degerman, Sofie
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi. Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi.
    Rydén, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Combining epigenetic and clinicopathological variables improves prognostic prediction in clear cell Renal Cell CarcinomaManuskript (preprint) (Övrigt vetenskapligt)
  • 25.
    Andersson-Evelönn, Emma
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Vidman, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Källberg, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Landfors, Mattias
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Liu, Xijia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Ljungberg, Börje
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Hultdin, Magnus
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi.
    Rydén, Patrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Degerman, Sofie
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap, Patologi. Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi.
    Combining epigenetic and clinicopathological variables improves specificity in prognostic prediction in clear cell renal cell carcinoma2020Ingår i: Journal of Translational Medicine, ISSN 1479-5876, E-ISSN 1479-5876, Vol. 18, nr 1, artikel-id 435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Metastasized clear cell renal cell carcinoma (ccRCC) is associated with a poor prognosis. Almost one-third of patients with non-metastatic tumors at diagnosis will later progress with metastatic disease. These patients need to be identified already at diagnosis, to undertake closer follow up and/or adjuvant treatment. Today, clinicopathological variables are used to risk classify patients, but molecular biomarkers are needed to improve risk classification to identify the high-risk patients which will benefit most from modern adjuvant therapies. Interestingly, DNA methylation profiling has emerged as a promising prognostic biomarker in ccRCC. This study aimed to derive a model for prediction of tumor progression after nephrectomy in non-metastatic ccRCC by combining DNA methylation profiling with clinicopathological variables.

    Methods: A novel cluster analysis approach (Directed Cluster Analysis) was used to identify molecular biomarkers from genome-wide methylation array data. These novel DNA methylation biomarkers, together with previously identified CpG-site biomarkers and clinicopathological variables, were used to derive predictive classifiers for tumor progression.

    Results: The “triple classifier” which included both novel and previously identified DNA methylation biomarkers together with clinicopathological variables predicted tumor progression more accurately than the currently used Mayo scoring system, by increasing the specificity from 50% in Mayo to 64% in our triple classifier at 85% fixed sensitivity. The cumulative incidence of progress (pCIP5yr) was 7.5% in low-risk vs 44.7% in high-risk in M0 patients classified by the triple classifier at diagnosis.

    Conclusions: The triple classifier panel that combines clinicopathological variables with genome-wide methylation data has the potential to improve specificity in prognosis prediction for patients with non-metastatic ccRCC.

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  • 26.
    Angelchev Shiryaev, Artem
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Karlsson, Johan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Estimating Dependence Structures with Gaussian Graphical Models: A Simulation Study in R2021Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Graphical models are powerful tools when estimating complex dependence structures among large sets of data. This thesis restricts the scope to undirected Gaussian graphical models. An initial predefined sparse precision matrix was specified to generate multivariate normally distributed data. Utilizing the generated data, a simulation study was conducted reviewing accuracy, sensitivity and specificity of the estimated precision matrix. The graphical LASSO was applied using four different packages available in R with seven selection criteria's for estimating the tuning parameter.

    The findings are mostly in line with previous research. The graphical LASSO is generally faster and feasible in high dimensions, in contrast to stepwise model selection. A portion of the selection methods for estimating the optimal tuning parameter obtained the true network structure. The results provide an estimate of how well each model obtains the true, predefined dependence structure as featured in our simulation. As the simulated data used in this thesis is merely an approximation of real-world data, one should not take the results as the only aspect of consideration when choosing a model.

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  • 27.
    Angelov, Angel G.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Methods for interval-censored data and testing for stochastic dominance2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis includes four papers: the first three of them are concerned with methods for interval-censored data, while the forth paper is devoted to testing for stochastic dominance.

    In many studies, the variable of interest is observed to lie within an interval instead of being observed exactly, i.e., each observation is an interval and not a single value. This type of data is known as interval-censored. It may arise in questionnaire-based studies when the respondent gives an answer in the form of an interval without having pre-specified ranges. Such data are called self-selected interval data. In this context, the assumption of noninformative censoring is not fulfilled, and therefore the existing methods for interval-censored data are not necessarily applicable.

    A problem of interest is to estimate the underlying distribution function. There are two main approaches to this problem: (i) parametric estimation, which assumes a particular functional form of the distribution, and (ii) nonparametric estimation, which does not rely on any distributional assumptions. In Paper A, a nonparametric maximum likelihood estimator for self-selected interval data is proposed and its consistency is shown. Paper B suggests a parametric maximum likelihood estimator. The consistency and asymptotic normality of the estimator are proven.

    Another interesting problem is to infer whether two samples arise from identical distributions. In Paper C, nonparametric two-sample tests suitable for self-selected interval data are suggested and their properties are investigated through simulations.

    Paper D concerns testing for stochastic dominance with uncensored data. The paper explores a testing problem which involves four hypotheses, that is, based on observations of two random variables X and Y, one wants to discriminate between four possibilities: identical survival functions, stochastic dominance of X over Y, stochastic dominance of Y over X, or crossing survival functions. Permutation-based tests suitable for two independent samples and for paired samples are proposed. The tests are applied to data from an experiment concerning the individual's willingness to pay for a given environmental improvement.

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    spikblad
  • 28.
    Angelov, Angel G.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Nonparametric two-sample tests for informatively interval-censored dataManuskript (preprint) (Övrigt vetenskapligt)
  • 29.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Maximum likelihood estimation for survey data with informative interval censoring2019Ingår i: AStA Advances in Statistical Analysis, ISSN 1863-8171, E-ISSN 1863-818X, Vol. 103, nr 2, s. 217-236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interval-censored data may arise in questionnaire surveys when, instead of being asked to provide an exact value, respondents are free to answer with any interval without having pre-specified ranges. In this context, the assumption of noninformative censoring is violated, and thus, the standard methods for interval-censored data are not appropriate. This paper explores two schemes for data collection and deals with the problem of estimation of the underlying distribution function, assuming that it belongs to a parametric family. The consistency and asymptotic normality of a proposed maximum likelihood estimator are proven. A bootstrap procedure that can be used for constructing confidence intervals is considered, and its asymptotic validity is shown. A simulation study investigates the performance of the suggested methods.

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  • 30.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Nonparametric estimation for self-selected interval data collected through a two-stage approach2017Ingår i: Metrika (Heidelberg), ISSN 0026-1335, E-ISSN 1435-926X, Vol. 80, nr 4, s. 377-399Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Self-selected interval data arise in questionnaire surveys when respondents are free to answer with any interval without having pre-specified ranges. This type of data is a special case of interval-censored data in which the assumption of noninformative censoring is violated, and thus the standard methods for interval-censored data (e.g. Turnbull's estimator) are not appropriate because they can produce biased results. Based on a certain sampling scheme, this paper suggests a nonparametric maximum likelihood estimator of the underlying distribution function. The consistency of the estimator is proven under general assumptions, and an iterative procedure for finding the estimate is proposed. The performance of the method is investigated in a simulation study.

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  • 31.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Tests of stochastic dominance with repeated measurements data2023Ingår i: AStA Advances in Statistical Analysis, ISSN 1863-8171, E-ISSN 1863-818X, Vol. 107, nr 3, s. 443-467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper explores a testing problem which involves four hypotheses, that is, based on observations of two random variables X and Y, we wish to discriminate between four possibilities: identical survival functions, stochastic dominance of X over Y, stochastic dominance of Y over X, or crossing survival functions. Four-decision testing procedures for repeated measurements data are proposed. The tests are based on a permutation approach and do not rely on distributional assumptions. One-sided versions of the Cramér–von Mises, Anderson–Darling, and Kolmogorov–Smirnov statistics are utilized. The consistency of the tests is proven. A simulation study shows good power properties and control of false-detection errors. The suggested tests are applied to data from a psychophysical experiment.

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  • 32.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Kriström, Bengt
    Department of Forest Economics, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nilsson, Mats E.
    Gösta Ekman Laboratory, Department of Psychology, Stockholm University, Stockholm, Sweden.
    Four-decision tests for stochastic dominance, with an application to environmental psychophysics2019Ingår i: Journal of mathematical psychology (Print), ISSN 0022-2496, E-ISSN 1096-0880, Vol. 93, artikel-id 102281Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    If the survival function of a random variable X lies to the right of the survival function of a random variable Y, then X is said to stochastically dominate Y. Inferring stochastic dominance is particularly complicated because comparing survival functions raises four possible hypotheses: identical survival functions, dominance of X over Y, dominance of Y over X, or crossing survival functions. In this paper, we suggest four-decision tests for stochastic dominance suitable for paired samples. The tests are permutation-based and do not rely on distributional assumptions. One-sided Cramér–von Mises and Kolmogorov–Smirnov statistics are employed but the general idea may be utilized with other test statistics. The power to detect dominance and the different types of wrong decisions are investigated in an extensive simulation study. The proposed tests are applied to data from an experiment concerning the individual’s willingness to pay for a given environmental improvement.

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  • 33.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Kriström, Bengt
    Umeå universitet, Samhällsvetenskapliga fakulteten, Centrum för miljö- och naturresursekonomi (CERE). Department of Forest Economics, Swedish University of Agricultural Sciences.
    Nilsson, Mats E.
    Gösta Ekman Laboratory, Department of Psychology, Stockholm University.
    Testing for stochastic dominance: Procedures with four hypothesesManuskript (preprint) (Övrigt vetenskapligt)
  • 34.
    Angelov, Angel G.
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Probability, Operations Research and Statistics, Faculty of Mathematics and Informatics, Sofia University St. Kliment Ohridski, Sofia, Bulgaria.
    Ekström, Magnus
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Puzon, Klarizze
    United Nations University World Institute for Development Economics Research, Helsinki, Finland.
    Arcenas, Agustin
    School of Economics, University of the Philippines, Diliman, Quezon City, Philippines.
    Kriström, Bengt
    Department of Forest Economics, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Quantile regression with interval-censored data in questionnaire-based studies2022Ingår i: Computational statistics (Zeitschrift), ISSN 0943-4062, E-ISSN 1613-9658Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interval-censored data can arise in questionnaire-based studies when the respondent gives an answer in the form of an interval without having pre-specified ranges. Such data are called self-selected interval data. In this case, the assumption of independent censoring is not fulfilled, and therefore the ordinary methods for interval-censored data are not suitable. This paper explores a quantile regression model for self-selected interval data and suggests an estimator based on estimating equations. The consistency of the estimator is shown. Bootstrap procedures for constructing confidence intervals are considered. A simulation study indicates satisfactory performance of the proposed methods. An application to data concerning price estimates is presented.

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  • 35.
    Annelin, Alice
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Nationalekonomi.
    Svanström, Tobias
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Nationalekonomi. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Department of Accounting and Operations Management, BI Norwegian Business School, Oslo, Norway.
    The Triggers and Consequences of Audit Team Stress: qualitative evidence from engagement teams2022Ingår i: International Journal of Auditing, ISSN 1090-6738, E-ISSN 1099-1123, Vol. 26, nr 2, s. 113-133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study investigates audit team stress, its triggers and consequences to provide qualitative evidence about what audit team stress is and how its triggers and consequences can influence team stress and audit quality. Audit teams in three different audit firms, including different audit team ranks, discussed team stress experiences from one specific engagement during group and individual interviews. Audit work can be stressful, and its consequences can threaten audit quality. Additionally, shared team stress differs from individual personal stress. This research discusses how audit team stress, its triggers and consequences can occur at an interteam stress level, when all team members experience the same stress, and at an intrateam stress level, when individuals feel stress from a team experience. Contributions are made to audit literature and practitioners about audit experiences at a team level and its influence on audit quality, including new insights about time budget pressures and auditor affect.

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  • 36.
    Arnelo, Urban
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Division of Surgery, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden.
    Valente, Roberto
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Division of Surgery, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden; Division of Surgical Oncology, Department of Surgery, University of Colorado School of Medicine, Aurora, CO, USA.
    Scandavini, Chiara Maria
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Halimi, Asif
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Division of Surgery, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden.
    Mucelli, Raffaella M.Pozzi
    Department of Radiology Huddinge, Karolinska University Hospital, O-huset 42, Stockholm, Sweden; Division of Radiology, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden.
    Rangelova, Elena
    Division of Surgery, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden; Section for Upper Abdominal Surgery at Department of Surgery, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Svensson, Johan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Schulick, Richard D.
    Division of Surgical Oncology, Department of Surgery, University of Colorado School of Medicine, CO, Aurora, United States.
    Torphy, Robert J.
    Division of Surgical Oncology, Department of Surgery, University of Colorado School of Medicine, CO, Aurora, United States.
    Fagerström, Niklas
    Department of Upper GI Diseases, Karolinska University Hospital, Stockholm, Sweden.
    Moro, Carlos Fernández
    Department of Clinical Pathology and Cancer Diagnostics, Karolinska University Hospital, Huddinge, Sweden; Department of Laboratory Medicine, Division of Pathology, Karolinska Institutet, Huddinge, Sweden.
    Vujasinovic, Miroslav
    Department of Upper GI Diseases, Karolinska University Hospital, Stockholm, Sweden.
    Matthias Löhr, Johannes
    Division of Surgery, Department of Clinical Science, Intervention, and Technology (CLINTEC), Karolinska Institutet, Stockholm, Sweden; Department of Upper GI Diseases, Karolinska University Hospital, Stockholm, Sweden.
    Del Chiaro, Marco
    Division of Surgical Oncology, Department of Surgery, University of Colorado School of Medicine, CO, Aurora, United States.
    Intraoperative pancreatoscopy can improve the detection of skip lesions during surgery for intraductal papillary mucinous neoplasia: a pilot study2023Ingår i: Pancreatology (Print), ISSN 1424-3903, E-ISSN 1424-3911, Vol. 23, nr 6, s. 704-711Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: Intraoperative pancreatoscopy is a promising procedure that might guide surgical resection for suspected main duct (MD) and mixed type (MT) intraductal papillary mucinous neoplasms (IPMNs). The aim of the present study was to assess the diagnostic yield and clinical impact of intraoperative pancreatoscopy in patients operated on for MD and MT-IPMNs.

    Methods: This is a retrospective cohort study. Patients undergoing surgery for suspected MD or MT-IPMN underwent intraoperative pancreatoscopy and frozen section analysis. In all patients who required extended resection due to pancreatoscopic findings, we compared the final histology with the results of the intraoperative frozen section analysis.

    Results: In total, 46 patients, 48% females, mean age (range) 67 years (45–82 years) underwent intraoperative pancreatoscopy. No mortality or procedure related complications were observed. Pancreatoscopy changed the operative course in 30 patients (65%), leading to extended resections in 20 patients (43%) and to parenchyma sparing procedures in 10 patients (22%). Analyzing the group of patients who underwent extended resections, 7 (35%) displayed lesions that needed further surgical treatment (six high grade dysplasia and one with G1 pancreatic neuroendocrine tumor) and among those 7, just 1 (14%) would have been detected exclusively with histological frozen section analysis of the transection margin. The combination of both pancreatoscopy and frozen section analysis lead to 86% sensitivity and 92% specificity for the detection of pathological tissue in the remnant pancreas.

    Conclusion: Intraoperative pancreatoscopy is a safe and feasible procedure and might allow the detection of skip lesions during surgery for suspect MD-involving IPMNs.

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  • 37.
    Arvidsson, Dan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Cross-Platform Modelling for Human Activity Recognition System2018Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Human activity recognition (HAR) systems have a large set of potential applications in healthcare, e.g. fall detection and tracking physical activities. HAR systems based on wearable sensors have gained the most attraction, due to smartphones having these sensors embedded in them. This makes them a great candidate for collecting human activity sensor data. By utilizing the smartphone sensors, no other sensors need to be supplied and instead only a mobile application needs to be supplied. However, this comes with a trade-off, sensors embedded in smartphones display specific heterogeneity and biases, depending on platform and price range. Normally in such a scenario, multiple HAR systems have to be built and trained for each device. This is both a time consuming effort and gives no guarantees that the different systems will have similar activity recognition accuracy. Therefore, in this thesis, a HAR system is constructed, where classification methods and filtering techniques are explored and evaluated, in an effort to give some guidelines for how to construct a HAR system, that can be embedded in multiple platforms. This study shows that when considering a few common activities, this HAR system performs well even when sensor data is collected from multiple sources. Ensemble method AdaBoost, in combination with decision trees, gives the overall best performance. Filtering techniques, such as Butterworth and Chebyshev performs better than constant- and linear detrending. This is primarily due to their ability to distinguish between low frequency activities, such as standing and sitting. The best result in this study was given when combining Chebyshev filtering and AdaBoosted decision trees, with a F-score of 0.9877.

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  • 38.
    Arvidsson, Dan
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Westerlund, Fredrik
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Fjärranalys av skog med multivariata modeller2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
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  • 39.
    Arvidsson, Per
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Snickars, Samuel
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Molekylär klassificering av tjocktarmscancer: PAM-klusteranalys för identifiering av undergrupper2012Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Huvudsyftet med denna studie är att med hjälp av klusteranalys dela in en mängd tjocktarmscancerfall i undergrupper baserat på deras molekylära egenskaper. Materialet som används tillhandahålls av en forskningsgrupp vid Patologi, Institutionen för medicinsk biovetenskap, Umeå universitet, och består efter viss bearbetning av 455 observationer vilket är en större datamängd än flera liknande studier. De molekylära variabler som ligger till grund för klusterindelningen är nivån på CIMP (CpG Island Methylator Phenotype), MSI (Mikrosatellitinstabillitet), BRAF- och KRAS-mutationer. Dessa är kategoriska variabler och därför används PAM (Partitioning Around Medoids) som är en särskild klusterteknik lämpad vid data på varierade variabelnivåer. I det slutliga resultatet fås fyra undergrupper som representeras av olika kombinationer av utfallen på ovannämnda variabler. Klustren utvärderas bland annat genom att jämföra överlevnadstiden för varje kluster, och det visar sig att två av klustren skiljer sig signifikant åt i detta avseende. Även andra patientrelaterade och tumörspecifika egenskaper kopplas samman till de olika cancertyperna och testas om de förekommer i varierande utsträckning. Var någonstans tumören är placerad är till exempel signifikant skilt mellan grupperna. Klusteranalyser är explorativa redskap så valet av variabler och sedermera tolkningar av resultat kan vara komplicerade och kräva stor sakkunskap.

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  • 40.
    Asad, Danna
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Styrke, Johan
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Hagsheno, Mohammad
    Johansson, Markus
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Huge, Ylva
    Svensson, Johan
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Pelander, Sofia
    Lauer, Jan
    Netterling, Hans
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    Aljabery, Firas
    Sherif, Amir
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Urologi och andrologi.
    A prospective multicenter study of visual response-evaluation by cystoscopy in patients undergoing neoadjuvant chemotherapy for muscle invasive urinary bladder cancer2022Ingår i: Scandinavian journal of urology, ISSN 2168-1805, E-ISSN 2168-1813, Vol. 56, nr 1, s. 20-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PURPOSE: To evaluate a method of transurethral visual response-staging in patients with urothelial muscle-invasive urinary bladder cancer (MIBC), undergoing neoadjuvant chemotherapy (NAC) and radical cystectomy (RC).

    METHODS: A prospective study at four Swedish cystectomy centers, cystoscopy was performed after final NAC-cycle for MIBC. Fifty-six participants underwent cystoscopy for visual staging of the tumor immediately pre-RC. Visual assessments were correlated to pathoanatomical outcomes post-RC.

    RESULTS: Seventeen tumors were classified as complete response (CR), i.e. pT0. Twenty-five patients had residual MIBC and 14 had non-muscle invasive residual tumors (NMIBC). Of the 39 patients with residual tumor, 25 were correctly identified visually (64%). Eleven patients were pN+. The diagnostic accuracy of cystoscopy to correctly identify complete response or remaining tumor was 70% (CI = 56-81%) with a sensitivity of 64% (CI = 47-79%), specificity 82% (CI = 57-96%), PPV 89% (CI = 74-96%) and NPV 50% (CI =38-61%). Twenty-eight cystoscopy evaluations showed signs of residual tumors and 3/28 (11%) were false positive. In 4/14 patients assessed having residual NMIBC the estimates were correct, 8/14 had histopathological MIBC and 2/14 had CR. In 11/14 patients (79%), the suggested visual assessment of MIBC was correct, 2/14 had NMIBC and 1/14 had CR. Twenty-eight cystoscopies had negative findings, 14 were false negatives (50%), when cystoscopy falsely predicted pT0. Among them there were eight patients with pTa, pT1 or pTis and six MIBC-tumors. In 17 patients with histopathological pT0, 14 were correctly identified with cystoscopy (82%).

    CONCLUSION: Cystoscopy after the final NAC-cycle cannot robustly differentiate between NAC-responders and non-responders. Visually, negative MIBC-status cannot be determined safely.

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  • 41. Asberg, Signild
    et al.
    Eriksson, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Henriksson, Karin M
    Terént, Andreas
    Reduced risk of death with warfarin: results of an observational nationwide study of 20 442 patients with atrial fibrillation and ischaemic stroke2013Ingår i: International Journal of Stroke, ISSN 1747-4930, E-ISSN 1747-4949, Vol. 8, nr 8, s. 689-695Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND: Warfarin is demonstrated to be superior in efficacy over antiplatelet agents for the prevention of stroke, but the relationship between warfarin and mortality is less clear. Our aim was to investigate this relationship in a large cohort of unselected patients with atrial fibrillation and ischaemic stroke.

    METHODS: This observational study was based on patients who were discharged alive and registered in the Swedish Stroke Register in 2001 through 2005. Vital status was retrieved by linkage to the Swedish Cause of Death Register. We calculated a propensity score for the likelihood of warfarin prescription at discharge from hospital. The risk of death and 95% confidence intervals were estimated in Cox regression models.

    RESULTS: Out of the 20 442 patients with atrial fibrillation and ischaemic stroke (mean age = 79·5 years), 31% (n = 6399) were prescribed warfarin. After adjustment for the propensity score, warfarin was associated with a reduced risk of death (0·67; 95% confidence interval, 0·63-0·71). The crude rate (per 100 person-years) of fatal non-haemorrhagic stroke was lower in patients who received warfarin (1·60; 95% confidence interval, 1·34-1·89) compared to those who received antiplatelet (6·83; 95% confidence interval, 6·42-7·25). The rates (per 100 person-years) of fatal haemorrhagic stroke were 0·21 (95% confidence interval, 0·12-0·32) and 0·43 (95% confidence interval, 0·34-0·55) in patients prescribed warfarin and antiplatelet therapy, respectively.

    CONCLUSIONS: In addition to its established benefit for stroke prevention, warfarin therapy in patients with atrial fibrillation and ischaemic stroke was associated with a reduced risk of death, without an increased risk of fatal haemorrhagic stroke.

  • 42.
    Asplund, Kjell
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Eriksson, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Persson, Olle
    Umeå universitet, Samhällsvetenskapliga fakulteten, Sociologiska institutionen.
    Country comparisons of human stroke research since 2001: a bibliometric study2012Ingår i: Stroke, ISSN 0039-2499, E-ISSN 1524-4628, Vol. 43, nr 3, s. 830-837Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND AND PURPOSE: This is the first bibliometric comparison between countries of the development of stroke research over time.

    METHODS: Clinical and epidemiological articles on stroke published 2001 to mid-2011 were identified in Science Citation Index Expanded. Article fractions, citation fractions, h-index, and international collaboration were calculated using the BibExcel software and adjusted for population size and gross domestic product.

    RESULTS: The United States dominated with 28.7% of the sum of article fractions and 36.2% of the sum of citation fractions. The United States, Japan, the United Kingdom, and Germany together accounted for 52.1% of articles and 61.0% of citations. When adjusted for population size or gross domestic product, several small European countries, together with Israel and Taiwan, ranked the highest. Per population, there was a negative association (r=0.60) between burden of stroke (disability-adjusted life-years lost) and number of articles per population. In China, South Korea, and Singapore, the annual growth of stroke articles was more than twice the worldwide average. Whereas multinational collaboration was common within Europe and North America, it was relatively uncommon between Asian countries.

    CONCLUSIONS: The Big 4 in scientific literature on stroke, as to both number of articles and citations, are the United States, Japan, the United Kingdom, and Germany. Many small European countries have, in relation to their size, a high scientific production. Several countries with rapidly expanding economies have very fast growth of scientific production on stroke. Our results emphasize the need for stroke research in countries with a high population burden of stroke and they highlight the role of multinational collaboration.

  • 43. Babb, Penny
    et al.
    Zhang, Li-Chun
    Allin, Paul
    Wallgren, Anders
    Wallgren, Britt
    Blunt, Gordon
    Garrett, Andrew
    Murtagh, Fionn
    Smith, Peter W. F.
    Elliott, Duncan
    Nason, Guy
    Powell, Ben
    Moore, Jamie C.
    Durrant, Gabriele B.
    Smith, Paul A.
    Chambers, Raymond L.
    Herzberg, Agnes M.
    Pilling, Mark
    Appleby, Wendy
    Barnett, Arthur
    Bhansali, Rajendra
    Bharadwaj, Neeraj
    Dong, Yuexiao
    van den Brakel, J. A.
    Budd, Lisa
    Doidge, James
    Gilbert, Ruth
    Francis, Brian
    Frisoli, Kayla
    Nugent, Rebecca
    Garcia Perez, Francisco Javier
    Lara, Libia
    Porcu, Emilio
    Henry, Sarah
    Hunt, Ian
    Ieva, Francesca
    Gasperoni, Francesca
    Jansson, Ingegerd
    Kumar, Kuldeep
    Longford, Nick
    Manninen, Asta
    Mateu, Jorge
    McNicholas, Paul D.
    McNicholas, Sharon M.
    Tait, Peter A.
    Mehew, Jenny
    Oberski, Daniel L.
    Ruiz, Marcelo
    Yohai, Victor J.
    Zamar, Ruben
    Stehlik, Milan
    Stehlikova, Silvia
    Nunez Soza, Ludy
    Towers, Jude
    Wijayatunga, Priyantha
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Statistical challenges of administrative and transaction data: Discussion on the paper by Hand2018Ingår i: Journal of the Royal Statistical Society: Series A (Statistics in Society), ISSN 0964-1998, E-ISSN 1467-985X, Vol. 181, nr 3, s. 578-605Artikel i tidskrift (Övrigt vetenskapligt)
  • 44.
    Back, Erik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Brännström, Fredrik
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Department of Surgery, Södertälje Hospital, Södertälje, Sweden.
    Svensson, Johan
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Rutegård, Jörgen
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Matthiessen, Peter
    Haapamäki, Markku M
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Rutegård, Martin
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Umeå universitet, Medicinska fakulteten, Wallenberg centrum för molekylär medicin vid Umeå universitet (WCMM).
    Mucosal blood flow in the remaining rectal stump is more affected by total than partial mesorectal excision in patients undergoing anterior resection: a key to understanding differing rates of anastomotic leakage?2021Ingår i: Langenbeck's archives of surgery (Print), ISSN 1435-2443, E-ISSN 1435-2451, Vol. 406, nr 6, s. 1971-1977Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PURPOSE: Anterior resection is the procedure of choice for tumours in the mid and upper rectum. Depending on tumour height, a total mesorectal excision (TME) or partial mesorectal excision (PME) can be performed. Low anastomoses in particular have a high risk of developing anastomotic leakage, which might be explained by blood perfusion compromise. A pilot study indicated a worse blood flow in TME patients in an open setting. The aim of this study was to further evaluate perianastomotic blood perfusion changes in relation to TME and PME in a predominantly laparoscopic context.

    METHOD: In this prospective cohort study, laser Doppler flowmetry was used to evaluate the perianastomotic colonic and rectal perfusion before and after surgery. The two surgical techniques were compared in terms of mean differences of perfusion units using a repeated measures ANOVA design, which also enabled interaction analyses between type of mesorectal excision and location of measurement. Anastomotic leakage until 90 days after surgery was reported for descriptive purposes.

    RESULTS: Some 28 patients were available for analysis: 17 TME and 11 PME patients. TME patients had a reduced blood perfusion postoperatively compared to PME patients in the aboral posterior area (mean difference: -57 vs 18 perfusion units; p = 0.010). An interaction between mesorectal excision type and anterior/posterior location was detected at the aboral level (p = 0.007). Two patients developed a minor leakage, diagnosed after discharge.

    CONCLUSION: Patients operated on using TME have a decreased blood flow in the aboral posterior quadrant of the rectum postoperatively compared to patients operated on using PME. This might explain differing rates of anastomotic leakage.

    TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02401100.

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  • 45.
    Back, Erik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Häggström, Jenny
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Holmgren, Klas
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Haapamäki, Markku M
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Matthiessen, P.
    Rutegård, Jörgen
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Rutegård, Martin
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Umeå universitet, Medicinska fakulteten, Wallenberg centrum för molekylär medicin vid Umeå universitet (WCMM).
    Permanent stoma rates after anterior resection for rectal cancer: risk prediction scoring using preoperative variables2021Ingår i: British Journal of Surgery, ISSN 0007-1323, E-ISSN 1365-2168, Vol. 108, nr 11, s. 1388-1395Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND: A permanent stoma after anterior resection for rectal cancer is common. Preoperative counselling could be improved by providing individualized accurate prediction modelling.

    METHODS: Patients who underwent anterior resection between 2007 and 2015 were identified from the Swedish Colorectal Cancer Registry. National Patient Registry data were added to determine presence of a stoma 2 years after surgery. A training set based on the years 2007-2013 was employed in an ensemble of prediction models. Judged by the area under the receiving operating characteristic curve (AUROC), data from the years 2014-2015 were used to evaluate the predictive ability of all models. The best performing model was subsequently implemented in typical clinical scenarios and in an online calculator to predict the permanent stoma risk.

    RESULTS: Patients in the training set (n = 3512) and the test set (n = 1136) had similar permanent stoma rates (13.6 and 15.2 per cent). The logistic regression model with a forward/backward procedure was the most parsimonious among several similarly performing models (AUROC 0.67, 95 per cent c.i. 0.63 to 0.72). Key predictors included co-morbidity, local tumour category, presence of metastasis, neoadjuvant therapy, defunctioning stoma use, tumour height, and hospital volume; the interaction between age and metastasis was also predictive.

    CONCLUSION: Using routinely available preoperative data, the stoma outcome at 2 years after anterior resection for rectal cancer can be predicted fairly accurately.

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  • 46.
    Back, Erik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Häggström, Jenny
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Holmgren, Klas
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Haapamäki, Markku M
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Matthiessen, Peter
    Department of Surgery, Faculty of Medicine and Health, School of Health and Medical Sciences, Örebro University, Sweden.
    Rutegård, Jörgen
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi.
    Rutegård, Martin
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Kirurgi. Umeå universitet, Medicinska fakulteten, Wallenberg centrum för molekylär medicin vid Umeå universitet (WCMM).
    Author response to: Permanent stoma prediction after anterior resection for rectal cancer: risk prediction scoring using preoperative variables2022Ingår i: British Journal of Surgery, ISSN 0007-1323, E-ISSN 1365-2168, Vol. 109, nr 2, s. e40-e40Artikel i tidskrift (Refereegranskat)
  • 47.
    Backman, Annica
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Sjögren, Karin
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Lindkvist, Marie
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Epidemiologi och global hälsa. Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Lövheim, Hugo
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering.
    Edvardsson, David
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad. School of Nursing and Midwifery, La Trobe University, Melbourne, Australia.
    Characteristics of highly rated leadership in nursing homes using item response theory2017Ingår i: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 73, nr 12, s. 2903-2913Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aim: To identify characteristics of highly rated leadership in nursing homes. Background: An ageing population entails fundamental social, economic and organizational challenges for future aged care. Knowledge is limited of both specific leadership behaviours and organizational and managerial characteristics which have an impact on the leadership of contemporary nursing home care. Design: Cross-sectional. Method: From 290 municipalities, 60 were randomly selected and 35 agreed to participate, providing a sample of 3605 direct-care staff employed in 169 Swedish nursing homes. The staff assessed their managers' (n = 191) leadership behaviours using the Leadership Behaviour Questionnaire. Data were collected from November 2013 - September 2014, and the study was completed in November 2016. A two-parameter item response theory approach and regression analyses were used to identify specific characteristics of highly rated leadership. Results: Five specific behaviours of highly rated nursing home leadership were identified; that the manager: experiments with new ideas; controls work closely; relies on subordinates; coaches and gives direct feedback; and handles conflicts constructively. The regression analyses revealed that managers with social work backgrounds and privately run homes were significantly associated with higher leadership ratings. Conclusion: This study highlights the five most important leadership behaviours that characterize those nursing home managers rated highest in terms of leadership. Managers in privately run nursing homes and managers with social work backgrounds were associated with higher leadership ratings. Further work is needed to explore these behaviours and factors predictive of higher leadership ratings.

  • 48.
    Backman, Annica
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Sjögren, Karin
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Lindkvist, Marie
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik. Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Epidemiologi och global hälsa.
    Lövheim, Hugo
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering.
    Edvardsson, David
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad. School of Nursing and Midwifer y, La Trobe University, Melbourne, VIC, Australia.
    Towards person-centredness in aged-care: exploring the impact of leadership2016Ingår i: Journal of Nursing Management, ISSN 0966-0429, E-ISSN 1365-2834, Vol. 24, nr 6, s. 766-774Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aim: To explore the association between leadership behaviours among managers in aged care, and person‐centredness of care and the psychosocial climate.

    Background: Theory suggests that leadership is important for improving person‐centredness in aged care, however, empirical evidence is lacking.

    Methods: A cross‐sectional design was used to collect data from Swedish aged care staff (= 3661). Valid and reliable questionnaires assessing leadership behaviours, person‐centeredness of care and the psychosocial climate were used. Data were analysed using multiple linear regression including interaction terms.

    Results: Leadership behaviours were significantly related to the person‐centredness of care and the psychosocial climate. The level of person‐centredness of care moderated the impact of leadership on the psychosocial climate.

    Conclusions and implications for nursing management: The leadership behaviour of managers significantly impacts person‐centred care practice and contributes to the psychosocial climate for both staff and residents in aged care. This study is the first empirically to confirm that middle managers have a central leadership role in developing and supporting person‐centred care practice, thereby creating a positive psychosocial climate and high quality care.

  • 49.
    Backman, Helena
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Avdelningen för hållbar hälsa.
    Blomberg, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Lundquist, Anders
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Strandkvist, Viktor
    Department of Health and Technology, Luleå University of Technology, Luleå, Sweden.
    Sawalha, Sami
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Nilsson, Ulf
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Eriksson Ström, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Hedman, Linnea
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Avdelningen för hållbar hälsa.
    Stridsman, Caroline
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Rönmark, Eva
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Avdelningen för hållbar hälsa.
    Lindberg, Anne
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin.
    Lung function trajectories and associated mortality among adults with and without airway obstruction2023Ingår i: American Journal of Respiratory and Critical Care Medicine, ISSN 1073-449X, E-ISSN 1535-4970, Vol. 208, nr 10, s. 1063-1074Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rationale: Spirometry is essential for diagnosis and assessment of prognosis in COPD.

    Objectives: To identify FEV1 trajectories and their determinants, based on annual spirometry measurements among individuals with and without airway obstruction. Furthermore, to assess mortality in relation to trajectories.

    Methods: In 2002-04, individuals with airway obstruction (AO) (FEV1/VC<0.70, n=993) and age- and sex-matched non-obstructive (NO) referents were recruited from population-based cohorts. Annual spirometries until 2014 were utilized in joint-survival Latent Class Mixed Models to identify lung function trajectories. Mortality data were collected during 15 years of follow-up.

    Results: Three trajectories were identified among the AO-cases and two among the NO referents. Trajectory membership was driven by baseline FEV1%predicted (%pred) in both groups and additionaly, pack-years in AO and current smoking in NO. Longitudinal FEV1%pred level depended on baseline FEV1%pred, pack-years and obesity. The trajectories were distributed: 79.6% T1AO FEV1-high with normal decline, 12.8% T2AO FEV1-high with rapid decline, and 7.7% T3AO FEV1-low with normal decline (mean 27, 72 and 26 mL/year) among AO-individuals, and 96.7% T1NO FEV1-high with normal decline and 3.3% T2NO FEV1-high with rapid decline (mean 34 and 173 mL/year) among referents. Hazard for death was increased for T2AO (HR1.56) and T3AO (HR3.45) vs. T1AO, and for T2NO (HR2.99) vs. T1NO.

    Conclusions: Three different FEV1 trajectories were identified among those with airway obstruction and two among the referents, with different outcomes in terms of FEV1-decline and mortality. The FEV1 trajectories among airway obstructive and the relationship between low FVC and trajectory outcome are of particular clinical interest.

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  • 50.
    Baranowska-Rataj, Anna
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Sociologiska institutionen.
    De Luna, Xavier
    Umeå universitet, Samhällsvetenskapliga fakulteten, Handelshögskolan vid Umeå universitet, Statistik.
    Ivarsson, Anneli
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Epidemiologi och global hälsa.
    Does the number of siblings affect health in midlife?: Evidence from the Swedish Prescribed Drug Register2016Ingår i: Demographic Research, ISSN 1435-9871, Vol. 35, s. 1259-1302, artikel-id 43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: In many societies, growing up in a large family is associated with receiving less parental time, attention, and financial support. As a result, children with a large number of siblings may have worse physical and mental health outcomes than children with fewer siblings.

    Objective: Our objective is to examine the long-term causal effects of sibship size on physical and mental health in modern Sweden.

    Methods: We employ longitudinal data covering the entire Swedish population from the Multigenerational Register and the Medical Birth Register. This data includes information on family size and on potential confounders such as parental background. We use the Prescribed Drug Register to identify the medicines that have been prescribed and dispensed. We use instrumental variable models with multiple births as instruments to examine the causal effects of family size on the health outcomes of children, as measured by receiving medicines at age 45.

    Results: Our results indicate that in Sweden, growing up in a large family does not have a detrimental effect on physical and mental health in midlife.

    Contribution: We provide a systematic overview of the health-related implications of growing up in a large family. We adopt a research design that gives us the opportunity to make causal inferences about the long-term effects of family size. Moreover, our paper provides evidence on the links between family size and health outcomes in the context of a developed country that implements policies oriented towards reducing social inequalities in health and other living conditions.

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