ArticleBiometrics2020
Power calculation for cross-sectional stepped wedge cluster randomized trials with variable cluster sizes.
Article in Biometrics, 2020. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 15 papers.
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Who cites it
15 citing papers in PubMed.
- Integrating Nonpharmacological Options Into Perioperative Pain Care: A Cluster Randomized Clinical Trial.JAMA network open · 2026Trial
- The batched stepped wedge design: A design robust to delays in cluster recruitment.Statistics in medicine · 2022Trial
- Design and monitoring of randomized trials in vision research with binary endpoints.Clinical trials (London, England) · 2026Article
- What scientific inferences can be made with randomized implementation rollout trials.Implementation science : IS · 2025Article
- Selecting the optimal longitudinal cluster randomized design with a continuous outcome: Parallel-arm, crossover, or stepped-wedge.Statistical methods in medical research · 2025Article
- Reconsidering stepped wedge cluster randomized trial designs with implementation periods: Fewer sequences or the parallel-group design with baseline and implementation periods are potentially more efficient.Clinical trials (London, England) · 2024Article
- Optimal designs using generalized estimating equations in cluster randomized crossover and stepped wedge trials.Statistical methods in medical research · 2024Article
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- Stepped Wedge Cluster Randomized Trials: A Methodological Overview.World neurosurgery · 2022Review
- Impact of unequal cluster sizes for GEE analyses of stepped wedge cluster randomized trials with binary outcomes.Biometrical journal. Biometrische Zeitschrift · 2022Article
- Power calculation for analyses of cross-sectional stepped-wedge cluster randomized trials with binary outcomes via generalized estimating equations.Statistics in medicine · 2021Article
- Mixed-effects models for the design and analysis of stepped wedge cluster randomized trials: An overview.Statistical methods in medical research · 2021Review
- Methods for dealing with unequal cluster sizes in cluster randomized trials: A scoping review.PloS one · 2021Article
- Explaining the variation in the attained power of a stepped-wedge trial with unequal cluster sizes.BMC medical research methodology · 2020Article
Corrections and comments
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Authors and funding
3 authors.
Funding
Abstract
Standard sample size calculation formulas for stepped wedge cluster randomized trials (SW-CRTs) assume that cluster sizes are equal. When cluster sizes vary substantially, ignoring this variation may lead to an under-powered study. We investigate the relative efficiency of a SW-CRT with varying cluster sizes to equal cluster sizes, and derive variance estimators for the intervention effect that account for this variation under a mixed effects model-a commonly used approach for analyzing data from cluster randomized trials. When cluster sizes vary, the power of a SW-CRT depends on the order in which clusters receive the intervention, which is determined through randomization. We first derive a variance formula that corresponds to any particular realization of the randomized sequence and propose efficient algorithms to identify upper and lower bounds of the power. We then obtain an "expected" power based on a first-order approximation to the variance formula, where the expectation is taken with respect to all possible randomization sequences. Finally, we provide a variance formula for more general settings where only the cluster size arithmetic mean and coefficient of variation, instead of exact cluster sizes, are known in the design stage. We evaluate our methods through simulations and illustrate that the average power of a SW-CRT decreases as the variation in cluster sizes increases, and the impact is largest when the number of clusters is small.
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