Abstract:
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.
journal_name
Biometricsjournal_title
Biometricsauthors
Shardell MD,El-Kamary SSdoi
10.1111/j.1541-0420.2008.01114.xsubject
Has Abstractpub_date
2009-06-01 00:00:00pages
635-9issue
2eissn
0006-341Xissn
1541-0420pii
BIOM1114journal_volume
65pub_type
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