• Felizitas A Eichner, Groenwold Rolf H H RHH Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, the Netherlands; Department of Clinical Epidemiolog, Diederick E Grobbee, and Katrien Oude Rengerink.
• Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, the Netherlands. Electronic address: felizitas.eichner@uni-wuerzburg.de.
• J Clin Epidemiol. 2019 Mar 1; 107: 89-100.

ObjectiveTo determine how often stepped-wedge cluster randomized controlled trials reach their planned sample size, and what reasons are reported for choosing a stepped-wedge trial design.Study Design And SettingWe conducted a PubMed literature search (period 2012 to 2017) and included articles describing the results of a stepped-wedge cluster randomized trial. We calculated the percentage of studies reaching their prespecified number of participants and clusters, and we summarized the reasons for choosing the stepped-wedge trial design as well as difficulties during enrollment.ResultsForty-six individual stepped-wedge studies from a total of 53 articles were included in our review. Of the 35 studies, for which recruitment rate could be calculated, 69% recruited their planned number of participants, with 80% having recruited the planned number of clusters. Ethical reasons were the most common motivation for choosing the stepped-wedge trial design. Most important difficulties during study conduct were dropout of clusters and delayed implementation of the intervention.ConclusionAbout half of recently published stepped-wedge trials reached their planned sample size indicating that recruitment is also a major problem in these trials. Still, the stepped-wedge trial design can yield practical, ethical, and methodological advantages.Copyright © 2018 Elsevier Inc. All rights reserved.

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