Characteristics of randomised trials on diseases in the digestive system registered in ClinicalTrials.gov: a retrospective analysis

Abstract

Objectives

To evaluate the adequacy of reporting of protocols for randomised trials on diseases of the digestive system registered in http://ClinicalTrials.gov and the consistency between primary outcomes, secondary outcomes and sample size specified in http://ClinicalTrials.gov and published trials.

Methods

Randomised phase III trials on adult patients with gastrointestinal diseases registered before January 2009 in http://ClinicalTrials.gov were eligible for inclusion. From http://ClinicalTrials.gov all data elements in the database required by the International Committee of Medical Journal Editors (ICMJE) member journals were extracted. The subsequent publications for registered trials were identified. For published trials, data concerning publication date, primary and secondary endpoint, sample size, and whether the journal adhered to ICMJE principles were extracted. Differences between primary and secondary outcomes, sample size and sample size calculations data in http://ClinicalTrials.gov and in the published paper were registered.

Results

105 trials were evaluated. 66 trials (63%) were published. 30% of trials were registered incorrectly after their completion date. Several data elements of the required ICMJE data list were not filled in, with missing data in 22% and 11%, respectively, of cases concerning the primary outcome measure and sample size. In 26% of the published papers, data on sample size calculations were missing and discrepancies between sample size reporting in http://ClinicalTrials.gov and published trials existed.

Conclusion

The quality of registration of randomised controlled trials still needs improvement.

Article summary

Article focus

• Outcome reporting bias is a considerable problem.

• A number of journals (International Committee of Medical Journal Editors journals) only publish clinical trials that are registered in relevant trial databases such as http://ClinicalTrials.gov before recruitment of participants. Older trials commenced after 1 July 2005 will be considered for publication only if they are adequately registered before journal submission.

• Previous studies of published trials suggest that many are registered inadequately.

Key messages

• A number of trials are registered inadequately in http://ClinicalTrials.gov without information about basic methodological issues.

• Several trials published in journals that require registration in online databases are registered after their date of completion.

• Discrepancies between the registered information in trial registrations and the trial publications still exist (such as the planned sample size calculations).

Strength and limitations of this study

• The study is small, only evaluating 105 trials. The real extent of inadequate trial registration may be under- or overestimated.

• Only trials concerning gastrointestinal diseases were evaluated, which makes it difficult to generalise to other medical specialties.