An approach to estimate between- and within-group correlation coefficients in multicenter studies: plasma carotenoids as biomarkers of intake of fruits and vegetables
2005 (English)In: American Journal of Epidemiology, ISSN 0002-9262, E-ISSN 1476-6256, Vol. 162, no 6, 591-598 p.Article in journal (Refereed) PublishedText
In a multicenter study, the overall correlation between two variables can be broken down into a within- and a between-group correlation reflecting associations at the individual and aggregate levels, respectively. A random-effects model is used to estimate variance components of nutrition-related variables and the within- and between-group correlation coefficients. Using data from the European Prospective Investigation into Cancer and Nutrition (EPIC), the authors analyzed the association between levels of three plasma carotenoids (alpha-carotene, beta-cryptoxanthin, and lycopene) and dietary intake of three items (total fruits, carrots, and tomatoes), assessed through dietary questionnaire and single 24-hour dietary recall measurements, in a cross-sectional study involving 3,089 subjects from nine European countries. Intraclass correlation coefficients were 0.178 for alpha-carotene, 0.216 for beta-cryptoxanthin, and 0.299 for lycopene. The between-group correlation coefficients were higher than the within-group coefficients for all three carotenoids. For beta-cryptoxanthin and fruit intake, the between-group versus the within-group correlations were 0.78 and 0.26 for the dietary questionnaire and 0.85 and 0.19 for the 24-hour dietary recall. Results indicate that variability of exposure is driven mainly by the individual compared with the aggregate variation and that biomarker levels perform fairly accurately in discriminating population-level consumption of fruits and vegetables.
Place, publisher, year, edition, pages
Cary: Oxford University Press, 2005. Vol. 162, no 6, 591-598 p.
carotenoids, diet, epidemiologic methods, multicenter studies, random-effects model
Public Health, Global Health, Social Medicine and Epidemiology
IdentifiersURN: urn:nbn:se:umu:diva-120402DOI: 10.1093/aje/kwi242ISI: 000231695000013PubMedID: 16093290OAI: oai:DiVA.org:umu-120402DiVA: diva2:935431