Abstract

The cluster randomized one-way crossover design, known as a stepped-wedge design, is becoming increasingly popular, especially for health studies in less industrialized countries. This design, however, presents numerous challenges, both for design and analysis.

Two issues regarding the design of a stepped-wedge study will be highlighted: randomization and power. Specifically, first, there is the question of how best to constrain the randomization so that it is balanced over time with respect to covariates-a highly constrained but ad hoc procedure will be presented. Second, the various pieces of information necessary for a full power calculation will be delineated.

As with cluster-randomized designs in general, close attention must be given to study hypotheses of interest, and the relation of these to the two levels of intervention-cluster and individual. A study of isoniazid prophylaxis implementation in 29 clinics in Rio de Janeiro is used to exemplify the range of questions that can arise. A few analyses of the data are also presented, so as to illustrate the degree to which data analytic choices to address these questions can vary the results, and to show the longitudinal complexities that need be considered.