A popular design choice in public health and implementation science research, stepped wedge cluster randomized trials (SW-CRTs) are a form of randomized trial whereby clusters are progressively transitioned from control to intervention, and the timing of transition is randomized for each cluster. An important task at the design stage is to ensure that the planned trial has sufficient power to observe a clinically meaningful effect size. While methods for determining study power have been well-developed for SW-CRTs with continuous and binary outcomes, limited methods for power calculation are available for SW-CRTs with censored time-to-event outcomes. In this article, we propose a stratified marginal Cox model to account for secular trend in cross-sectional SW-CRTs, and derive an explicit expression of the robust sandwich variance to facilitate power calculations without the need for computationally intensive simulations. Power formulas based on both the Wald and robust score tests are developed and compared via simulation, generally demonstrating superiority of robust score procedures in different finite-sample scenarios. Finally, we illustrate our methods using a SW-CRT testing the effect of a new electronic reminder system on time to catheter removal in hospital settings. We also offer an R Shiny application to facilitate sample size and power calculations using our proposed methods.

翻译：在公共卫生和实施科学研究中，阶梯楔形群组随机试验（SW-CRTs）是一种流行的设计选择，它通过逐步将群组从对照组过渡到干预组，且每个群组的过渡时间随机化。设计阶段的关键任务是确保计划中的试验具有足够的统计效能，以检测具有临床意义的效应量。尽管针对连续性和二分类结局的SW-CRTs的效能计算方法已较为成熟，但对于存在删失的时间至事件结局，可用的效能计算方法仍十分有限。本文提出一种分层边际Cox模型，以控制跨断面SW-CRTs中的时间趋势，并推导出稳健三明治方差的显式表达式，从而无需依赖计算密集的模拟即可进行效能计算。我们基于Wald检验和稳健得分检验分别推导了效能公式，并通过模拟比较显示，稳健得分程序在不同有限样本情景中通常更具优势。最后，我们通过一项测试新型电子提醒系统对医院内导管移除时间影响的SW-CRT研究示例，阐明了所提方法的实际应用。同时，我们提供了一个R Shiny应用程序，以支持基于所提方法进行样本量和效能计算。