Factors affecting power in stepped wedge trials when the treatment effect varies with time
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处理效应随时间变化时阶梯楔形试验检验功效的影响因素
- 研究问题
- 阶梯楔形整群随机试验中，当处理效应随暴露时间变化时，目标效应、试验设计与分析模型如何影响检验功效和样本需求？
- 方法与思路
- 作者使用公开功效计算软件与模拟，对比即时恒定效应模型和暴露时间指标模型，并考察不同时间平均效应及设计调整。
- 材料陈述的贡献
- 摘要称，常见设计转换模型后维持九成功效通常需将样本增至原来的 1.5 至 3 倍，甚至更多；短期效应通常更易检出。
- 阅读关注点
- 核对效应随暴露时间变化的设定、时间平均区间和相关结构，并检查增加基线样本或前后测量时点的功效差异。
- 阅读边界
- 这是 arXiv 预印本，同行评审及期刊接收未核实，且所给摘要被截断；样本膨胀倍数只适用于文中设定，后续结论未知。
原文摘要
Stepped wedge cluster randomized trials (SW-CRTs) have historically been analyzed using immediate treatment (IT) models, which assume the effect of the treatment is immediate after treatment initiation and subsequently remains constant over time. However, recent research has shown that this assumption can lead to severely misleading results if treatment effects vary with exposure time, i.e. time since the intervention started. Models that account for time-varying treatment effects, such as the exposure time indicator (ETI) model, allow researchers to target estimands such as the time-averaged treatment effect (TATE) over an interval of exposure time, or the point treatment effect (PTE) representing a treatment contrast at one time point. However, this increased flexibility results in reduced power. In this paper, we use public power calculation software and simulation to characterize factors affecting SW-CRT power. Key elements include choice of estimand, study design considerations, and analysis model selection. or common SW-CRT designs, the sample size (clusters per sequence or individuals per cluster-period) must be increased substantially, commonly by a factor of 1.5 to 3, but often by much more, to maintain 90\% power when switching from an IT model to an ETI model (targeting the TATE over the study). However, the inflation factor is lower for TATE estimands over shorter periods that exclude longer exposure times. In general, SW-CRT designs (including the "staircase" variant) have much greater power for estimating "short-term effects" relative to "long-term effects". For an ETI model targeting a TATE estimand, substantial power can be gained by adding time points to the start of the study or increasing baseline sample size, but surprisingly little power is gained from adding time points to the end of the study. More restrictive choices for modeling the exposure... [truncated]