Projects per year
Abstract
Trial planning requires making efficient yet practical design choices. In a cluster randomized crossover trial, clusters of subjects cross back and forth between implementing the control and intervention conditions over the course of the trial, with each crossover marking the start of a new period. If it is possible to set up such a trial with more crossovers, a pertinent question is whether there are efficiency gains from clusters crossing over more frequently, and if these gains are substantial enough to justify the added complexity and cost of implementing more crossovers. We seek to determine the optimal number of crossovers for a fixed trial duration, and then identify other highly efficient designs by allowing the total number of clusters to vary and imposing thresholds on maximum cost and minimum statistical power. Our results pertain to trials with continuous recruitment and a continuous primary outcome, with the treatment effect estimated using a linear mixed model. To account for the similarity between subjects' outcomes within a cluster, we assume a correlation structure in which the correlation decays gradually in a continuous manner as the time between subjects' measurements increases. The optimal design is characterized by crossovers between the control and intervention conditions with each successive subject. However, this design is neither practical nor costefficient to implement, nor is it necessary: the gains in efficiency increase sharply in moving from a twoperiod to a fourperiod trial design, but approach an asymptote for the scenarios considered as the number of crossovers continues to increase.
Original language  English 

Pages (fromto)  50215033 
Number of pages  13 
Journal  Statistics in Medicine 
Volume  38 
Issue number  25 
DOIs  
Publication status  Published  10 Nov 2019 
Keywords
 cluster crossover
 cluster randomized trial
 continuous recruitment design
 correlation decay
 linear mixed model
 optimal design
Projects
 1 Finished

New methods and guidelines for the design, analysis and reporting of clustercrossover and stepped wedge randomised trials in clinical and public health research
Forbes, A., Carlin, J. B., Haines, T., Hemming, K., Kahan, B. & McKenzie, J.
National Health and Medical Research Council (NHMRC) (Australia)
1/01/16 → 31/12/18
Project: Research