Objectives To identify factors associated with discrepant outcome reporting in randomized drug trials. Study Design and Setting Cohort study of protocols submitted to a Swiss ethics committee 1988–1998: 227 protocols and amendments were compared with 333 matching articles published during 1990–2008. Discrepant reporting was defined as addition, omission, or reclassification of outcomes. Results Overall, 870 of 2,966 unique outcomes were reported discrepantly (29.3%). Among protocol-defined primary outcomes, 6.9% were not reported (19 of 274), whereas 10.4% of reported outcomes (30 of 288) were not defined in the protocol. Corresponding percentages for secondary outcomes were 19.0% (284 of 1,495) and 14.1% (334 of 2,375). Discrepant reporting was more likely if P values were P ≥ 0.05 [adjusted odds ratio (aOR): 1.38; 95% confidence interval (CI): 1.07, 1.78], more likely for efficacy compared with harm outcomes (aOR: 2.99; 95% CI: 2.08, 4.30) and more likely for composite than for single outcomes (aOR: 1.48; 95% CI: 1.00, 2.20). Cardiology (aOR: 2.34; 95% CI: 1.44, 3.79) and infectious diseases (aOR: 1.77; 95% CI: 1.01, 3.13) had more discrepancies compared with all specialties combined. Conclusion Discrepant reporting was associated with statistical significance of results, type of outcome, and specialty area. Trial protocols should be made freely available, and the publications should describe and justify any changes made to protocol-defined outcomes.
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