title: How many subjects are needed in a longitudinal birth cohort study?
abstract: One of the first decisions that needs to be taken when planning a birth cohort concerns the size of the study. This in turn will depend on the research questions to be answered and thence whether environmental exposures and outcomes are measured on a continuum or as dichotomous variables. Here we describe ways in which different birth cohorts have addressed this issue and explore the advantages of smaller detailed studies over larger less-detailed studies.
authors.affiliation: Centre for Child and Adolescent Health, Department of Community Based Medicine, University of Bristol, Bristol, UK. jean.golding@bristol.ac.uk
authors.forename: Jean
authors.initials: J
authors.lastname: Golding
authors.forename: Colin
authors.initials: C
authors.lastname: Steer
mesh_terms: D002657:Child Development; D015331:Cohort Studies; D004781:Environmental Exposure / Q000517:prevention & control*; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D011247:Pregnancy; D011314:Preventive Health Services / Q000458:organization & administration*; D012107:Research Design / Q000706:statistics & numerical data*; D018401:Sample Size