Treatment effect sizes vary in randomized trials depending on the type of outcome measure

Dorthe B. Berthelsen, Elisabeth Ginnerup-Nielsen, Carsten Juhl, Hans Lund, Marius Henriksen, Asbjørn Hróbjartsson, Sabrina M. Nielsen, Marieke Voshaar, Robin Christensen*

*Corresponding author for this work

Research output: Contribution to journalReview articleAcademicpeer-review

6 Citations (Scopus)
12 Downloads (Pure)


Objective: To compare estimated treatment effects of physical therapy (PT) between patient-reported outcome measures (PROMs) and outcomes measured in other ways.

Study Design and Setting: We selected randomized trials of PT with both a PROM and a non-PROM included in Cochrane systematic reviews (CSRs). Two reviewers independently extracted data and risk-of-bias assessments. Our primary outcome was the ratio of odds ratios (RORs), used to quantify how effect varies between PROMs and non-PROMs; an ROR > 1 indicates larger effect when assessed by using PROMs. We used REML-methods to estimate associations of trial characteristics with effects and between-trial heterogeneity.

Results: From 90 relevant CSRs, 205 PT trials were included. The summary ROR across all the comparisons was not statistically significant (ROR, 0.88 [95% CI: 0.70–1.12]; P = 0.30); however, the heterogeneity was substantial (I2 = 88.1%). When stratifying non-PROMs further into clearly objective non-PROMs (e.g., biomarkers) and other non-PROMs (e.g., aerobic capacity), the PROMs appeared more favorable than did clearly objective non-PROMs (ROR, 1.92 [95% CI: 0.99–3.72]; P = 0.05).

Conclusion: Estimated treatment effects based on PROMs are generally comparable with treatment effects measured in other ways. However, in our study, PROMs indicate a more favorable treatment effect compared with treatment effects based on clearly objective outcomes.

Original languageEnglish
Pages (from-to)27-38
Number of pages12
JournalJournal of clinical epidemiology
Publication statusPublished - Jul 2020


  • Effect size
  • Meta-epidemiology
  • Meta-Research
  • Patient-involvement
  • Patient-reported outcome measures
  • Physical therapy
  • n/a OA procedure


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