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OBJECTIVE: Availability of randomized controlled trial (RCT) protocols is essential for the interpretation of trial results and research transparency. STUDY DESIGN AND SETTING: In this study, we determined the availability of RCT protocols approved in Switzerland, Canada, Germany and the UK in 2012. For these RCTs, we searched PubMed, Google Scholar, Scopus, and trial registries for publicly available protocols and corresponding full-text publications of results. We determined the proportion of RCTs with: (1) publicly available protocols, (2) publications citing the protocol, and (3) registries providing a link to the protocol. A multivariable logistic regression model explored factors associated with protocol availability. RESULTS: 326 RCTs were included of which 118 (36.2 %) made their protocol publicly available; 56 (47.6% 56/118) as a peer-reviewed publications and 48 (40.7%, 48/118) provided as supplementary material. 90.9% (100/110) of the protocols were cited in the main publication and 55.9% (66/118) were linked in clinical trial registry. Larger sample size (>500; OR 5.90, 95% CI, 2.75-13.31) and investigator-sponsorship (OR 1.99, 95% CI, 1.11-3.59) were associated with increased protocol availability. Most protocols were made available shortly before the publication of the main results. CONCLUSION: RCT protocols should be made available at an early stage of the trial.

Original publication




Journal article


J clin epidemiol

Publication Date



Randomized controlled trials, meta-research, protocol publication, transparency, trial protocols, trial registration