Outcome Reporting bias in Exercise Oncology trials (OREO): a cross-sectional study

Abstract

Abstract Background Despite evidence of selective outcome reporting across multiple disciplines, this has not yet been assessed in trials studying the effects of exercise in people with cancer. Therefore, the purpose of our study was to explore prospectively registered randomised controlled trials (RCTs) in exercise oncology for evidence of selective outcome reporting. Methods Eligible trials were RCTs that 1) investigated the effects of at least partially supervised exercise interventions in people with cancer; 2) were preregistered (i.e. registered before the first patient was recruited) on a clinical trials registry; and 3) reported results in a peer-reviewed published manuscript. We searched the PubMed database from the year of inception to September 2020 to identify eligible exercise oncology RCTs clinical trial registries. Eligible trial registrations and linked published manuscripts were compared to identify the proportion of sufficiently preregistered outcomes reported correctly in the manuscripts, and cases of outcome omission, switching, and silently introduction of non-novel outcomes. Results We identified 31 eligible RCTs and 46 that were ineligible due to retrospective registration. Of the 405 total prespecified outcomes across the 31 eligible trials, only 6.2% were preregistered complete methodological detail. Only 16% (n=148/929) of outcomes reported in published results manuscripts were linked with sufficiently preregistered outcomes without outcome switching. We found 85 total cases of outcome switching. A high proportion (41%) of preregistered outcomes were omitted from the published results manuscripts, and many published outcomes (n=394; 42.4%) were novel outcomes that had been silently introduced (median, min-max=10, 0-50 per trial). We found no examples of preregistered efficacy outcomes that were measured, assessed, and analysed as planned. Conclusions We found evidence suggestive of widespread selective outcome reporting and non-reporting bias (outcome switching, omitted preregistered outcomes, and silently introduced novel outcomes). The existence of such reporting discrepancies has implications for the integrity and credibility of RCTs in exercise oncology. Preregistered protocol https://osf.io/dtkar/ (posted: November 19, 2019)

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