Pre-trial systematic reviews to justify a new randomised trial and inform its design: proposal for a new review method

One or more systematic reviews of the evidence before launching a new trial serve to document that the clinical question is not answered already in previous trials and to inform the optimal design choices for the new trial. It is rarely documented that thorough systematic reviews are undertaken, and one main reason may be that it is very time and resource demanding to conduct a regular systematic review. To overcome this challenge, we propose a new type of review: the pre-trial systematic review. This review type aims to deliver a comprehensive, but not exhaustive, compendium of existing (published, completed, ongoing, or planned) trials, which can form the basis for deciding whether further trials are needed. The pre-trial systematic review methodology leverages any prior available reviews and clinical trial registries to compile a focused overview of existing trials. In contrast to a traditional systematic review, further assessments and analyses in pre-trial systematic reviews focus exclusively on those defining outcomes that are crucial to decide whether a new trial is needed. After deciding whether a new trial is needed, the overview may be used to justify how the trial should be designed, and it may act as a primer for more exhaustive traditional systematic reviews on the topic.