title: Sizing a trial to alter the trajectory of health behaviours: methods, parameter estimates, and their application.
abstract: Group-randomized trials often involve repeat observations on the same participants. When there are no more than two observations from each participant, standard mixed-model regression methods for a pretest-posttest design can be used. When there are more than two observations from each participant, random coefficients models may be useful. This paper describes the random coefficients analysis appropriate to data from an extended nested cohort design and presents the methods for power analysis and sample size calculations based on that analysis. We provide estimates for the parameters required for those calculations for a number of adolescent health behaviours. We also show how the estimates can be used to plan a future trial.
authors.affiliation: Division of Epidemiology, School of Public Health, The Ohio State University, B222 Starling Loving Hall, 320 West 10th Street, Columbus, OH 43210, USA. dmurray@sph.osu.edu
authors.forename: David M
authors.initials: DM
authors.lastname: Murray
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Blitstein
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hannan
authors.forename: William L
authors.initials: WL
authors.lastname: Baker
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Lytle
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D002648:Child; D005260:Female; D015438:Health Behavior; D006801:Humans; D008297:Male; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*; D018401:Sample Size; D014481:United States