Stepped wedge trials with continuous recruitment require new ways of thinking

Abstract

Objectives: There is substantial variation in the design of stepped wedge trials. Many recruit participants continuously over time, although the methodological literature has tended not to differentiate closely between continuous recruitment and discrete sampling. We argue for a deeper understanding of the special features of stepped wedge trials with continuous recruitment.

Study design and setting: This is a commentary and informal review.

Results: We discuss the scheduling of recruitment and implementation in continuous time and how contamination might be avoided. We also offer some suggestions on reporting and terminology for stepped wedge trials with continuous recruitment and comment on issues for analysis.

Conclusion: Repeated cross-section and continuous recruitment stepped wedge trials are not the same thing. More work is needed to develop the theory and practice of stepped wedge designs with continuous recruitment. Thoughtful approaches to design and clarity of reporting are vital.

Keywords: Cluster randomized trials; Contamination; Continuous recruitment; Interrupted time series; Stepped wedge.