• Merrick Zwarenstein, Kevin Thorpe, Shaun Treweek, and Kirsty Loudon.
• Centre for Studies in Family Medicine, Department of Family Medicine, Western University, London, Ontario, IC/ES, London, Ontario, Canada. Electronic address: merrick.zwarenstein@ices.on.ca.
• J Clin Epidemiol. 2020 Oct 1; 126: 202-206.

Background And ObjectivesA randomized controlled trial (RCT) may be intended either to support real-world decisions on choice between alternative interventions or to help researchers understand mechanisms of action of an intervention. PRECIS-2 is widely used to help investigators match detailed design elements to their main intention for that RCT. PRECIS-2 is increasingly being used retrospectively for assessing RCTs within reviews. In this commentary, we counter arguments that RCTs with a placebo control group, masking/blinding of participants or providers, or conducted in a single center should be retrospectively assessed as completely explanatory, overriding a detailed PRECIS-2 assessment. We also counter arguments that a trial cannot be assessed using only the main peer-reviewed trial report.Study Design And SettingThis is a commentary on the use of PRECIS-2 for systematic reviews.ResultsAlthough placebos are seldom openly prescribed in real-world care, knowing that an intervention achieves its impact via the placebo effect might change some clinical and policy decisions, which means that this feature does not always preclude decision-making use and so should not override a full PRECIS-2 assessment. A domain describing the comparator should be added to PRECIS-2. Conduct of an RCT in only a single centre should also not override PRECIS-2 as the decision support value of a single-centre RCT could be high for decision makers in that centre and others like it. Many journals require that submitted RCT reports meet CONSORT reporting guidelines, which standardizes the available information for all RCTs in systematic reviews; whereas information from registration and protocol documents is unstandardized and undermines comparison between RCTs and across reviews. Published RCT reports are thus more suitable for retrospective PRECIS-2 assessments, but PRECIS-2 domains with missing information should be scored as blank. Wider use of the CONSORT extension specific to pragmatic trials may reduce domains with missing data.ConclusionsPRECIS-2 can be used for retrospective assessments of trials in systematic reviews. The PRECIS-2 instrument should be expanded by including a domain describing the control group(s). Published RCT reports are suitable for retrospective PRECIS-2 assessments.Crown Copyright © 2020. Published by Elsevier Inc. All rights reserved.

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