[Roaming through methodology. XXVII. Problems with longitudinal studies: confounding of the relationship between age, time of measurement and birth cohort].
Nowadays, age-related research questions are investigated using longitudinal study designs where measurements are repeated over time in the same subjects. Cross-sectional studies are used less often for this purpose, as they provide measurements at only one point in time thus making it more difficult to establish relationships between variables and outcomes. However, longitudinal measurements also have drawbacks, even in investigations that, for example, are aimed at age-related changes in physical and psychosocial characteristics during growth and development in young people. In the study of age-related trends, several types of confounding may occur: birth cohort effects, time-of-measurement effects, and test-and-learning effects. If control measurements are carefully collected, for example, in a multiple longitudinal design, or by not repeatedly measuring a control group, the confounding may be quantified and the study results corrected accordingly.
Kemper
H C
HC
Vrije Universiteit, Faculteit der Geneeskunde, Instituut voor Extramuraal Geneeskundig Onderzoek, Amsterdam. hcg.kemper.emgo@med.vu.nl
D000367:Age Factors; D016022:Case-Control Studies; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D003430:Cross-Sectional Studies; D006801:Humans; D007858:Learning; D008137:Longitudinal Studies; D012107:Research Design / Q000592:standards*; D013997:Time Factors