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In stepped-wedge cluster randomized trials (SW-CRTs), clusters are randomized not to treatment and control arms, but to sequences dictating the times of crossing from control to intervention conditions. Randomization is an essential feature of this design but application of standard methods to promote and report on balance at baseline are not straightforward. We aimed to describe current methods of randomization and reporting of balance at baseline in SW-CRTs.
Study Design and Setting
We used electronic searches to identify primary reports of SW-CRTs published between 2016 and 2022.
Across 160 identified trials, the median number of clusters randomized was 11 (Q1-Q3: 8-18). Sixty-three (39%) used restricted randomization — most often stratification based on a single cluster-level covariate; 12 (19%) of these adjusted for the covariate(s) in the primary analysis. Overall, 50 (31%) and 134 (84%) reported on balance at baseline on cluster- and individual-level characteristics, respectively. Balance on individual-level characteristics was most often reported by condition in cross-sectional designs and by sequence in cohort designs. Authors reported baseline imbalances in 72 (45%) trials.
SW-CRTs often randomize a small number of clusters using unrestricted allocation. Investigators need guidance on appropriate methods of randomization and assessment and reporting of balance at baseline.
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Accepted: March 13, 2023
Received in revised form: March 9, 2023
Received: January 12, 2023
Publication stageIn Press Journal Pre-Proof
The authors declare that they have no conflicts of interest related to this article.
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