The quality of reporting participants’ baseline characteristics in randomised clinical trials: a scoping review of reviews

Abstract Background Reporting of baseline characteristics in randomised controlled trials (RCTs) is necessary to provide a clear and complete picture of the participants studied. The aim of this review was to map existing review-level evidence examining the quality of reporting of participant characteristics in any element of trials (encompassing reporting of baseline characteristics, their utilisation in statistical analyses and in assessment of generalisability of results). Methods This scoping review utilises Joanna Briggs Institute methodology. The searches were conducted in six electronic databases (MEDLINE, Embase, Cochrane Database of Systematic Reviews, Epistemonikos, Science Citation Index Expanded, ProQuest Dissertations & Theses) and included systematic reviews published in 2015–2025. We focused on baseline characteristics listed in the INCLUDE, PROGRESS-PLUS and PRO-EDI frameworks, or similar characteristics not specified in these frameworks. Results A total of 9634 records were screened, and 139 reviews (including 123 full-text papers) from a wide range of clinical areas were included. Reviews mainly focused on assessing the frequency of reporting baseline characteristics (118/123, 96%). Less attention was given to how these were measured or collected (76/123, 62%). The frequency of reporting demographic characteristics, in particular, sex/gender and race/ethnicity, was assessed more often (122/123, 99%) than socioeconomic characteristics (e.g. employment, residential status, income), reported in 66/123 (54%) reviews. The utilisation of baseline participant characteristics in statistical analyses (62/123, 50%) and generalisability of results assessment (19/123, 15%) was less frequently investigated. Conclusions There is a substantial body of review-level evidence focusing on the frequency of reporting participant demographic characteristics in RCTs. Further methodological research is required for socioeconomic characteristics, both how these are defined and utilised to inform future practice. Trial registration The review protocol was registered with the Open Science Framework ( https://doi.org/10.17605/OSF.IO/KZPBE ).