Premium
Calculating Sample Size for Studies with Expected All‐or‐None Nonadherence and Selection Bias
Author(s) -
Shardell Michelle D.,
ElKamary Samer S.
Publication year - 2009
Publication title -
biometrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.298
H-Index - 130
eISSN - 1541-0420
pISSN - 0006-341X
DOI - 10.1111/j.1541-0420.2008.01114.x
Subject(s) - selection bias , sample size determination , selection (genetic algorithm) , statistics , econometrics , mathematics , computer science , medicine , machine learning
Summary We develop sample size formulas for studies aiming to test mean differences between a treatment and control group when all‐or‐none nonadherence (noncompliance) and selection bias are expected. Recent work by Fay, Halloran, and Follmann (2007, Biometrics 63 , 465–474) addressed the increased variances within groups defined by treatment assignment when nonadherence occurs, compared to the scenario of full adherence, under the assumption of no selection bias. In this article, we extend the authors' approach to allow selection bias in the form of systematic differences in means and variances among latent adherence subgroups. We illustrate the approach by performing sample size calculations to plan clinical trials with and without pilot adherence data. Sample size formulas and tests for normally distributed outcomes are also developed in a Web Appendix that account for uncertainty of estimates from external or internal pilot data.