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Sizing a trial to alter the trajectory of health behaviours: methods, parameter estimates, and their application
Author(s) -
Murray David M.,
Blitstein Jonathan L.,
Hannan Peter J.,
Baker William L.,
Lytle Leslie A.
Publication year - 2006
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.2714
Subject(s) - trajectory , sizing , computer science , statistics , econometrics , mathematics , chemistry , physics , astronomy , organic chemistry
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. Copyright © 2006 John Wiley & Sons, Ltd.