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Multi-arm trials that use a parallel-group design and have three or more groups offer the opportunity to address more than one research question. They can speed up the evaluation of new interventions and facilitate head-to-head comparisons with competing treatment options. These trials appeal to clinicians and patients because they also increase the likelihood of receiving an experimental intervention rather than standard care.

Multi-arm parallel-group randomised clinical trials typically include multiple interventions, combinations of interventions, different doses of an intervention, a placebo and no intervention or treatment as usual. These elements can be combined in various ways resulting in numerous possible trial structures.

The Consolidated Standards of Reporting Trials (CONSORT) 2010 statement was developed to improve reporting of randomised clinical trials but focused primarily on parallel-group trials with two groups.

A special communication in JAMA presents an extension to the CONSORT 2010 statement checklist, as well as a number of recommendations and examples that provide specific guidance for the reporting of multi-arm parallel-group randomised clinical trials:

Lead author Ed Juszczak, Associate Professor and Director of the National Perinatal Epidemiology Unit’s Clinical Trials Unit, Nuffield Department of Population Health, said ‘Over the last 20 years, over 1 in 5 published trials were multi-arm trials. The extension aims to provide greater transparency and accuracy in the reporting of such trials to enhance understanding of the methodology and allow readers such as clinicians, journal editors, reviewers, guideline authors and funders to accurately assess the conduct of a trial and interpret the results.’

The extension recommends that multi-arm trials are identified as such and that the authors state clear objectives and hypotheses referring to all the treatment groups. Primary treatment comparisons should be identified and the planned, unplanned and exploratory comparisons should be reported completely and transparently. If statistical adjustments for multiplicity are applied, the rationale and method used should be described.

If periods of recruitment and follow-up are different across treatment groups (eg if groups were added or dropped) the periods and reasons for differences should be reported and any statistical implications addressed. Authors are also advised to indicate the number of treatment groups and include the word ‘randomised’ in the title and to document all planned comparisons in the protocol and statistical analysis plan.

Ed Juszczak said ‘This extension to the CONSORT 2010 statement checklist will enhance the reporting of multi-arm trials, and has an important educational role in improving their conduct. It therefore covers the overlapping areas of multi-arm trial methodology and reporting.’