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).

Changing patterns in reporting and sharing of review data in systematic reviews with meta-analysis of the effects of interventions: cross sectional meta-research study.

OBJECTIVES: To examine changes in completeness of reporting and frequency of sharing data, analytical code, and other review materials in systematic reviews over time; and factors associated with these changes. DESIGN: Cross sectional meta-research study. POPULATION: Random sample of 300 systematic reviews with meta-analysis of aggregate data on the effects of a health, social, behavioural, or educational intervention. Reviews were indexed in PubMed, Science Citation Index, Social Sciences Citation Index, Scopus, and Education Collection in November 2020. MAIN OUTCOME MEASURES: The extent of complete reporting and the frequency of sharing review materials in the systematic reviews indexed in 2020 were compared with 110 systematic reviews indexed in February 2014. Associations between completeness of reporting and various factors (eg, self-reported use of reporting guidelines, journal policies on data sharing) were examined by calculating risk ratios and 95% confidence intervals. RESULTS: Several items were reported suboptimally among 300 systematic reviews from 2020, such as a registration record for the review (n=113; 38%), a full search strategy for at least one database (n=214; 71%), methods used to assess risk of bias (n=185; 62%), methods used to prepare data for meta-analysis (n=101; 34%), and source of funding for the review (n=215; 72%). Only a few items not already reported at a high frequency in 2014 were reported more frequently in 2020. No evidence indicated that reviews using a reporting guideline were more completely reported than reviews not using a guideline. Reviews published in 2020 in journals that mandated either data sharing or inclusion of data availability statements were more likely to share their review materials (eg, data, code files) than reviews in journals without such mandates (16/87 (18%) v 4/213 (2%)). CONCLUSION: Incomplete reporting of several recommended items for systematic reviews persists, even in reviews that claim to have followed a reporting guideline. Journal policies on data sharing might encourage sharing of review materials.