CONSORT statement: extension to cluster randomised trials

Of 21 cluster trials identified in two major public health journals, only four (19%) had accounted for the clustering in the planning of the trial. 15 Similarly, in a review of physicians' patient care practices, 70% (38/54) of the identified studies had not appropriately accounted for the clustered nature of their study data in their analysis. 16 Of 16 cluster trials reviewed by Donner et al, only four provided any rationale for adopting a clustered design, only three accounted for clustering in the sample size calculations, and only eight accounted for clustering in the analysis. 17 Recent studies have shown continuing problems with the design and analysis of cluster trials; 42% (62/149) of trials of implementation research interventions did not account appropriately for the clustering in their design, 18 and 42% (10/24) of trials of clinical decision support systems did not appropriately account for clustering in their analysis (none accounted for clustering in their sample size calculations). Summary points Accurate reporting of trials is essential to ensure appropriate interpretation of results The CONSORT statement provides a framework for reporting individually randomised trials In some situations it is preferable to randomise groups of individuals (so called cluster randomised trials) Reports of cluster randomised trials require extra information on their special features The CONSORT statement has been extended to accommodate these features Inadequate methodological reporting of trials has been shown to be associated with bias in the estimate of treatment effects. 40 Use of the CONSORT statement for the reporting of two group parallel trials is associated with improved reporting quality. 41 42 43 We believe that the routine use of this proposed extension to the CONSORT statement will result in similar improvements for cluster trials.