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Attrition in Studies of Cognitive Aging
Umeå University, Faculty of Social Sciences, Umeå School of Business and Economics (USBE), Statistics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Bortfall i studier av kognitivt åldrande (Swedish)
Abstract [en]

Longitudinal studies of cognition are preferred to cross-sectional stud- ies, since they offer a direct assessment of age-related cognitive change (within-person change). Statistical methods for analyzing age-related change are widely available. There are, however, a number of challenges accompanying such analyzes, including cohort differences, ceiling- and floor effects, and attrition. These difficulties challenge the analyst and puts stringent requirements on the statistical method being used.

The objective of Paper I is to develop a classifying method to study discrepancies in age-related cognitive change. The method needs to take into account the complex issues accompanying studies of cognitive aging, and specifically work out issues related to attrition. In a second step, we aim to identify predictors explaining stability or decline in cognitive performance in relation to demographic, life-style, health-related, and genetic factors.

In the second paper, which is a continuation of Paper I, we investigate brain characteristics, structural and functional, that differ between suc- cessful aging elderly and elderly with an average cognitive performance over 15-20 years.

In Paper III we develop a Bayesian model to estimate the causal effect of living arrangement (living alone versus living with someone) on cog- nitive decline. The model must balance confounding variables between the two living arrangement groups as well as account for non-ignorable attrition. This is achieved by combining propensity score matching with a pattern mixture model for longitudinal data.

In paper IV, the objective is to adapt and implement available impu- tation methods to longitudinal fMRI data, where some subjects are lost to follow-up. We apply these missing data methods to a real dataset, and evaluate these methods in a simulation study.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2013. , 21 p.
Series
Statistical studies, ISSN 1100-8989 ; 47
Keyword [en]
Attrition, missing data, age-related cognitive change, non- ignorable dropout, monotone missing pattern, mixture models, pattern- mixture models, imputation
National Category
Other Social Sciences not elsewhere specified
Research subject
Statistics
Identifiers
URN: urn:nbn:se:umu:diva-82514ISBN: 978-91-7459-760-8 (print)OAI: oai:DiVA.org:umu-82514DiVA: diva2:661682
Public defence
2013-11-29, Humanisthuset, Hörsal F, Umeå universitet, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2013-11-08 Created: 2013-11-04 Last updated: 2016-03-07Bibliographically approved
List of papers
1. Genetic and lifestyle predictors of 15-Year longitudinal change in episodic memory
Open this publication in new window or tab >>Genetic and lifestyle predictors of 15-Year longitudinal change in episodic memory
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2012 (English)In: Journal of The American Geriatrics Society, ISSN 0002-8614, E-ISSN 1532-5415, Vol. 60, no 12, 2308-2312 p.Article in journal (Refereed) Published
Abstract [en]

OBJECTIVES: To reveal distinct longitudinal trajectories in episodic memory over 15 years and to identify demographic, lifestyle, health-related, and genetic predictors of stability or decline. DESIGN: Prospective cohort study. SETTING: The Betula Project, Umeå, Sweden. PARTICIPANTS: One thousand nine hundred fifty-four healthy participants aged 35 to 85 at baseline. MEASUREMENTS: Memory was assessed according to validated episodic memory tasks in participants from a large population-based sample. Data were analyzed using a random-effects pattern-mixture model that considered the effect of attrition over two to four longitudinal sessions. Logistic regression was used to determine significant predictors of stability or decline relative to average change in episodic memory. RESULTS: Of 1,558 participants with two or more test sessions, 18% were classified as maintainers and 13% as decliners, and 68% showed age-typical average change. More educated and more physically active participants, women, and those living with someone were more likely to be classified as maintainers, as were carriers of the met allele of the catechol-O-methyltransferase gene. Less educated participants, those not active in the labor force, and men were more likely to be classified as decliners, and the apolipoprotein E ɛ4 allele was more frequent in decliners. CONCLUSION: Quantitative, attrition-corrected assessment of longitudinal changes in memory can reveal substantial heterogeneity in aging trajectories, and genetic and lifestyle factors predict such heterogeneity.

National Category
Psychology (excluding Applied Psychology) Probability Theory and Statistics
Identifiers
urn:nbn:se:umu:diva-61415 (URN)10.1111/jgs.12000 (DOI)23110764 (PubMedID)
Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2017-12-07Bibliographically approved
2. Brain Characteristics of Individuals Resisting Age-Related Cognitive Decline over Two Decades
Open this publication in new window or tab >>Brain Characteristics of Individuals Resisting Age-Related Cognitive Decline over Two Decades
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2013 (English)In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 33, no 20, 8668-8677 p.Article in journal (Refereed) Published
Abstract [en]

Some elderly appear to resist age-related decline in cognitive functions, but the neural correlates of successful cognitive aging are not well known. Here, older human participants from a longitudinal study were classified as successful or average relative to the mean attrition-corrected cognitive development across 15-20 years in a population-based sample (n = 1561). Fifty-one successful elderly and 51 age-matched average elderly (mean age: 68.8 years) underwent functional magnetic resonance imaging while performing an episodic memory face-name paired-associates task. Successful older participants had higher BOLD signal during encoding than average participants, notably in the bilateral PFC and the left hippocampus (HC). The HC activation of the average, but not the successful, older group was lower than that of a young reference group (n = 45, mean age: 35.3 years). HC activation was correlated with task performance, thus likely contributing to the superior memory performance of successful older participants. The frontal BOLD response pattern might reflect individual differences present from young age. Additional analyses confirmed that both the initial cognitive level and the slope of cognitive change across the longitudinal measurement period contributed to the observed group differences in BOLD signal. Further, the differences between the older groups could not be accounted for by differences in brain structure. The current results suggest that one mechanism behind successful cognitive aging might be preservation of HC function combined with a high frontal responsivity. These findings highlight sources for heterogeneity in cognitive aging and may hold useful information for cognitive intervention studies.

National Category
Basic Medicine
Identifiers
urn:nbn:se:umu:diva-73534 (URN)10.1523/JNEUROSCI.2900-12.2013 (DOI)000319112600009 ()23678111 (PubMedID)
Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2017-12-06Bibliographically approved
3. Causal inference with longitudinal outcomes and non-ignorable drop-out: Estimating the effect of living alone on cognitive decline
Open this publication in new window or tab >>Causal inference with longitudinal outcomes and non-ignorable drop-out: Estimating the effect of living alone on cognitive decline
2016 (English)In: Journal of the Royal Statistic Society, Series C: Applied Statistics, ISSN 0035-9254, E-ISSN 1467-9876, Vol. 65, no 1, 131-144 p.Article in journal (Refereed) Published
Abstract [en]

We develop a model to estimate the causal effect of living arrangement (living alone versus living with someone) on cognitive decline based on a 15-year prospective cohort study, where episodic memory function is measured every 5 years. One key feature of the model is the combination of propensity score matching to balance confounding variables between the two living arrangement groups—to reduce bias due to unbalanced covariates at baseline, with a pattern–mixture model for longitudinal data—to deal with non-ignorable dropout. A fully Bayesian approach allows us to convey the uncertainty in the estimation of the propensity score and subsequent matching in the inference of the causal effect of interest. The analysis conducted adds to previous studies in the literature concerning the protective effect of living with someone, by proposing a modelling approach treating living arrangement as an exposure.

Keyword
Aging, Bayesian inference, Episodic memory, Non-ignorable missingness, Pattern–mixture model, Propensity score matching, Sensitivity
National Category
Probability Theory and Statistics Neurosciences
Research subject
Statistics
Identifiers
urn:nbn:se:umu:diva-82511 (URN)10.1111/rssc.12110 (DOI)000367978400007 ()
Projects
Statistiska metoder för studier av kognitiv åldrande: kognitionstester och hjärnavbildning
Funder
Swedish Research Council
Available from: 2013-11-04 Created: 2013-11-04 Last updated: 2017-12-06Bibliographically approved
4. Imputation of missing longitudinal fMRI data
Open this publication in new window or tab >>Imputation of missing longitudinal fMRI data
(English)Manuscript (preprint) (Other academic)
National Category
Neurosciences
Identifiers
urn:nbn:se:umu:diva-82512 (URN)
Available from: 2013-11-04 Created: 2013-11-04 Last updated: 2016-03-07Bibliographically approved

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