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Importance: Ceiling effect may lead to misleading conclusions when using patient-reported outcome measure (PROM) scores as an outcome.Objective: The aim of this study was to investigate the potential source of ceiling effect related errors in randomized controlled trials (RCTs) reporting no differences in patient-reported outcome measure (PROM) scores between study groups.Design: A review of RCTs published in the top 10 orthopedic journals was conducted, focusing on studies that reported no significant differences in outcomes between two study groups.All studies that reported no differences in PROM outcomes and used parametric statistical approach were included.The aim was to investigate the potential source of ceiling effect related errors-that is when the ceiling effect suppresses the possible difference between the groups.Setting: Review of RCTs published in the top 10 orthopedic journals according to their impact factors.Participants: RCTs published during 2012-2022 reporting no difference between the study groups in PROM scores and using parametric statistical approach were included to the analysis.Exposure: Distributions exceeding the PROM scales were analyzed from the included articles.Main Outcome: The proportions of patients exceeding the PROM scales were simulated using the observed dispersion parameters based on the assumed normal distribution, and the differences in the proportions between the study groups were subsequently analyzed. J o u r n a l P r e -p r o o fResults: After an initial screening of 2343 studies, 190 studies were included.The central 95% distribution of the scores exceeded the PROM scales in 140 (74%) of these studies.In 33 (17%) studies, the simulated patient proportions exceeding the scales indicated potential differences between the compared groups. Conclusion:It is common to have a mismatch between the chosen PROM instrument and the population being studied increasing a risk of an unjustified "no difference" conclusion due to a ceiling effect.Thus, a considerable ceiling effect should be considered a potential source of error. What is new?• In this systematic review, out of 190 included studies, 74% exhibited scores exceeding the PROM scales, indicating the presence of a ceiling effect.• A ceiling effect can prevent the detection of true differences between study groups, leading to unjustified conclusions.• Ceiling effect should be considered as a potential source of error when comparing PROM scores between groups.
Saarinen et al. (Wed,) studied this question.