OBJECTIVE: Interpreting a randomised trial requires access to more than the main results paper. We aimed to determine the: 1) proportion of trials referring to the protocol in the trial report and their accessibility; 2) proportion of protocols accessible from trial registry entry and by trial registration number search; and 3) types of additional publications associated with trial reports.
STUDY DESIGN AND SETTING: A previously-gathered sample of randomised trials of non-pharmacological interventions published in 2009 was used. Trial reports and registry entries were searched for protocol mentions and obtained when possible. Related publications were identified using citation searching.
RESULTS: Of 133 trials, 96 (72%) mentioned the protocol within the report, 61 (64%) contained details about protocol acquisition, with 48 (36%) protocols obtainable. Of the 129 registered trials, 32 (25%) had protocols obtainable from registry entry. Citation tracking identified 1030 related publications; secondary analyses and qualitative studies most common.
CONCLUSION: Trial protocols facilitate good trial conduct and interpretation. However, they are often not linked to the main report or registry and can be difficult to obtain. Many trials have related publications which are inconsistently linked. Trial registries and registration numbers could facilitate the threading of articles related to a trial, but currently do not.