Sample size and power analysis for stepped wedge cluster randomised trials with binary outcomes. Issue 2 (3rd April 2021)

• Record Type: Journal Article
• Authors: Wang, Jijia; Cao, Jing; Zhang, Song; Ahn, Chul
• Is Part Of: Statistical theory and related fields. Volume 5:Issue 2(2021)
• Page Start: 162
• Page End: 169
• Publication Date: 2021-04-03
• Subjects: Stepped wedge -- GEE -- clinical trials -- power analysis -- sample size; Statistics -- Periodicals; Statistics; Periodicals; Electronic journals; 001.422
• DOI: 10.1080/24754269.2021.1904094
• Languages: English
• ISSNs: 2475-4269

Abstract

Abstract : In stepped wedge cluster randomised trials (SW-CRTs), clusters of subjects are randomly assigned to sequences, where they receive a specific order of treatments. Compared to conventional cluster randomised studies, one unique feature of SW-CRTs is that all clusters start from control and gradually transition to intervention according to the randomly assigned sequences. This feature mitigates the ethical concern of withholding an effective treatment and reduces the logistic burden of implementing the intervention at multiple clusters simultaneously. This feature, however, presents challenges that need to be addressed in experimental design and data analysis, i.e., missing data due to prolonged follow-up and complicated correlation structures that involve between-subject and longitudinal correlations. In this study, based on the generalised estimating equation (GEE) approach, we present a closed-form sample size formula for SW-CRTs with a binary outcome, which offers great flexibility to account for unbalanced randomisation, missing data, and arbitrary correlation structures. We also present a correction approach to address the issue of under-estimated variance by GEE estimator when the sample size is small. Simulation studies and application to a real clinical trial are presented.