The relative efficiency of staircase and stepped wedge cluster randomised trial designs

The stepped wedge design is an appealing longitudinal cluster randomised trial design. However, it places a large burden on participating clusters by requiring all clusters to collect data in all periods of the trial. The staircase design may be a desirable alternative: treatment sequences consist of a limited number of measurement periods before and after implementation of the intervention. In this article we explore the relative efficiency of the stepped wedge design to several variants of the “basic staircase” design which has one control followed by one intervention period in each sequence. We model outcomes using linear mixed models and a sampling scheme where each participant is measured once. We first consider a basic staircase design embedded within the stepped wedge design, then basic staircase designs with the same total number of participants as the stepped wedge design, via either larger cluster-period sizes or additional clusters. The relative efficiency of the designs depends on the intracluster correlation structure, correlation parameters and the trial configuration, including the number of sequences and cluster-period size. For a wide range of realistic trial settings, a basic staircase design will deliver greater statistical power than a stepped wedge design for the same number of participants.