Linking ClinicalTrials.gov and PubMed to track results of interventional human clinical trials

Abstract

Objective: In an effort to understand how results of human clinical trials are made public, we analyze a large set of clinical trials registered at ClinicalTrials.gov, the world's largest clinical trial registry.

Materials and methods: We considered two trial result artifacts: (1) existence of a trial result journal article that is formally linked to a registered trial or (2) the deposition of a trial's basic summary results within the registry.

Results: The study sample consisted of 8907 completed, interventional, phase 2-or-higher clinical trials that were completed in 2006-2009. The majority of trials (72.2%) had no structured trial-article link present. A total of 2367 trials (26.6%) deposited basic summary results within the registry. Of those, 969 trials (10.9%) were classified as trials with extended results and 1398 trials (15.7%) were classified as trials with only required basic results. The majority of the trials (54.8%) had no evidence of results, based on either linked result articles or basic summary results (silent trials), while a minimal number (9.2%) report results through both registry deposition and publication.

Discussion: Our study analyzes the body of linked knowledge around clinical trials (which we refer to as the "trialome"). Our results show that most trials do not report results and, for those that do, there is minimal overlap in the types of reporting. We identify several mechanisms by which the linkages between trials and their published results can be increased.

Conclusion: Our study shows that even when combining publications and registry results, and despite availability of several information channels, trial sponsors do not sufficiently meet the mandate to inform the public either via a linked result publication or basic results submission.

Figure 1. Trial selection and analysis for presence of linked result article and basic results.

Figure 2. Diagram showing proportionally the overlap of trials with linked result article and trials with basic results and large proportion of silent trials with no linked result artifact.

Enlargement to the right illustrates the disproportionate publication rate (linked result article) between studies that have extended results, compared to those with only required results.