A cross-sectional audit showed that most Cochrane intervention reviews searched trial registers

Impact of searching clinical trials registers in systematic reviews of pharmaceutical and non-pharmaceutical interventions: Reanalysis of meta-analyses

Systematic reviewers are advised to search trials registers to minimise risk of reporting biases. However, there has been little research on the impact of searching trials registers on the results of meta-analyses. We aimed to evaluate the impact of searching clinical trials registers for systematic reviews of pharmaceutical or non-pharmaceutical interventions. We searched PubMed, Scopus, Science Citation Index and Social Sciences Citation Index, and Education Collection for systematic reviews with meta-analyses indexed from 2 November to 2 December 2020. A random sample of systematic reviews was initially drawn, and for reviews which considered randomised trials eligible for inclusion, which had not searched a trials register, we searched ClinicalTrials.gov, EudraCT, ANZCTR, and the WHO ICTRP search portal for eligible trials. We compared meta-analytic effect estimates before and after including results from additional trials identified. We found additional trials for 63% (63/101) of eligible reviews; however, trials with results that could contribute to a meta-analysis were identified for only 20% (20/101) of the reviews. On average, there was no difference in the meta-analytic effect estimates before versus after adding the new trials. In summary, searching clinical trial registers led to identification of additional trials for many reviews; however, very few trials had results available for inclusion in meta-analyses. Including results from the new trials led to no change in the meta-analytic estimates, on average. Trials registers would be even more valuable to systematic reviewers if more trialists made use of them (i.e., registered their trials and posted results in a timely manner).

A technical review of three clinical trials register resources indicates where improvements to the search interfaces are needed

Clinical trials registers form an important part of the search for studies in systematic reviews of intervention effectiveness but the search interfaces and functionality of registers can be challenging to search systematically and resource intensive to search well. We report a technical review of the search interfaces of three leading trials register resources: ClinicalTrials.gov, the EU Clinical Trials Register and the WHO International Clinical Trials Registers Platform. The technical review used a validated checklist to identify areas where the search interfaces of these trials register resources performed well, where performance was adequate, where performance was poor, and to identify differences between search interfaces. The review found low overall scores for each of the interfaces (ClinicalTrials.gov 55/165, the EU Clinical Trials Register 25/165, the WHO International Clinical Trials Registers Platform 32/165). This finding suggests a need for joined-up dialogue between the producers of the registers and researchers who search them via these interfaces. We also set out a series of four proposed changes which might improve the search interfaces. Trials registers are an invaluable resource in systematic reviews of intervention effectiveness. With the continued growth in systematic reviews, and initiatives such as 'AllTrials', there is an anticipated need for these resources. We conclude that small changes to the search interfaces, and improved dialogue with providers, might improve the future search functionality of these valuable resources.

An algorithm provided as initial guidance for reporting registry records and published protocols in systematic reviews

OBJECTIVE

We aim to synthesize the available guidance with existing practices by Cochrane reviewers to generate an algorithm as a starting point in assisting reviewers reporting of registry records and published protocols (TRRs/PPs) use in systematic reviews of interventions.

STUDY DESIGN

We used existing guidance from major review bodies, assessed the current reporting of TRRs/PPs use in a sample of Cochrane reviews, and engaged in critical analysis. Independent reviewers identified and extracted textual excerpts reporting the use of trial registry records and published protocols and codes following a systematic review framework. Based on these elements, and our initial research, we created an algorithm/graphical aid to visualize initial direction.

RESULTS

We included 166 Cochrane systematic reviews published between August 2015 and 2016 from 48 review groups. Review authors' terminology (e.g., ongoing, terminated) varied between and within reviews. Reporting practices were diverse and inconsistent.

CONCLUSIONS

This is a timely investigation in an era where evidence synthesis informs health and health care decisions. Our proposed algorithm provides initial direction to systematize the reporting of TRR/PP use. We hope that the algorithm generates further discussion to enhance the transparency of TRR/PP reporting and methodological research into the complexities of using protocols in systematic reviews of interventions.