Power and sample size calculation for stepped-wedge designs with discrete outcomes

Abstract

Background Stepped-wedge designs (SWD) are increasingly used to evaluate the impact of changes to the process of care within health care systems. However, to generate definitive evidence, a correct sample size calculation is crucial to ensure such studies are properly powered. The seminal work of Hussey and Hughes (Contemp Clin Trials 28(2):182–91, 2004) provides an analytical formula for power calculations with normal outcomes using a linear model and simple random effects. However, minimal development and evaluation have been done for power calculation with non-normal outcomes on their natural scale (e.g., logit, log). For example, binary endpoints are common, and logistic regression is the natural multilevel model for such clustered data. Methods We propose a power calculation formula for SWD with either normal or non-normal outcomes in the context of generalized linear mixed models by adopting the Laplace approximation detailed in Breslow and Clayton (J Am Stat Assoc 88(421):9–25, 1993) to obtain the covariance matrix of the estimated parameters. Results We compare the performance of our proposed method with simulation-based sample size calculation and demonstrate its use on a study of patient-delivered partner therapy for STI treatment and a study that assesses the impact of providing additional benchmark prevalence information in a radiologic imaging report. To facilitate adoption of our methods we also provide a function embedded in the R package “swCRTdesign” for sample size and power calculation for multilevel stepped-wedge designs. Conclusions Our method requires minimal computational power. Therefore, the proposed procedure facilitates rapid dynamic updates of sample size calculations and can be used to explore a wide range of design options or assumptions.

Bayesian optimal stepped wedge design

“…Methods to analyze stepped-wedge trials for binary responses using the generalized estimating equations (GEE) approach are discussed in Zhou et al (2020), Tian et al (2020), and Harrison and Wang (2021). Power and sample size calculations for a stepped-wedge trial with discrete outcomes are discussed in Xia et al (2021). Our approach can be extended to nonnormal responses in particular for responses with exponential family distribution.…”

“…Power and sample size calculations for a stepped‐wedge trial with discrete outcomes are discussed in Xia et al. (2021). Our approach can be extended to nonnormal responses in particular for responses with exponential family distribution.…”

Predictors of Oral Health Behaviors among Dental Students

“…There were 78 students enrolled in the 5th year, English section. Applying the calculation formula for a confidence level of p = 95%, z = 1.96, with a margin of error of 5%, a number of 65 students should participate in the study to be relevant from a statistical point of view [ 18 ]. Since several students expressed their desire to participate in the study, we enrolled all those who wished.…”

Knowledge Level on Infection Control among Romanian Undergraduate and Postgraduate Dental Students

“…According to the secretary of the Faculty of Dental Medicine within the “Grigore T. Popa” University of Medicine and Pharmacy from Iași, the total population of dental medical students in the dentistry program conducing to a Bachelor of Dentistry in Romanian language degree was 936 students [ 37 ]. The calculated sample size was made with a formula for confidence level of p = 95%, z = 1.96, with margin of error by 8%, by population size N = 936 [ 38 ]. The resulting calculated sample size was 130 students.…”