Cluster randomized trials in nursing homes should better be planned as open-cohort than as closed-cohort.

OBJECTIVES:Two designs are frequently used in cluster randomized trials in nursing homes: closed cohort and open cohort. The former design includes residents at the beginning of the trial and then follows them. In the latter design, participants are enrolled at the beginning of the trial or although it is ongoing; at dates of assessment, all residents present in the nursing home are assessed. The open-cohort design is much less used than the closed-cohort design, but it offers several advantages such as less exposure to individual attrition. Objective was to assess whether an open-cohort design could have been feasible in trials with a closed-cohort design. STUDY DESIGN AND SETTING:Twenty-two closed-cohort trials in nursing homes. RESULTS:An open-cohort design was considered a relevant alternative for 20 trials. For 16 trials, a resident newly admitted could not opt out of the intervention, and for all trials, the resident could benefit from an intervention effect if it existed. For two trials, newly admitted residents could not benefit from the intervention effect, if it existed. CONCLUSION:The open-cohort design is well-adapted for most of the interventions assessed in nursing homes by means of a cluster randomized trial and should be considered more often.