Cluster randomised trials: time for improvement

BMJ 1998;317:1171-1172 ( 31 October )

Editorials

Cluster randomised trials: time for improvement

The implications of adopting a cluster design are still largely being ignored

The first 150 words of the full text of this article appear below.

Cluster randomised trials, where groups of patients rather than individuals are randomised, are increasingly being used inhealth services research. Randomisation by individual is inappropriatefor evaluating some interventions, such as organisational changes,where it may not be feasible to randomise at the patient level.In such cases cluster randomisation at the level of the healthprofessional or organisation is necessary. Such randomisationcan also minimise the potential for contamination between treatmentswhen trial patients are managed within the samesetting.

The main consequence of adopting a cluster design is that the outcome for each patient can no longer be assumed to be independentof that for any other patient (which is the case in an individuallyrandomised trial). Patients within any one cluster are more likelyto have similar outcomes. For example, the management of patientswithin a single general practice is more likely to be consistentthan management . . . [Full text of this article]

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