Combining meta-epidemiological study datasets on commercial funding of randomised clinical trials: Database, methods, and descriptive results of the COMFIT study.

Randomised trials are often funded by commercial companies and methodological studies support a widely held suspicion that commercial funding may influence trial results and conclusions. However, these studies often have a risk of confounding and reporting bias. The risk of confounding is markedly reduced in meta-epidemiological studies that compare fairly similar trials within meta-analyses, and risk of reporting bias is reduced with access to unpublished data. Therefore, we initiated the COMmercial Funding In Trials (COMFIT) study aimed at investigating the impact of commercial funding on estimated intervention effects in randomised clinical trials based on a consortium of researchers who agreed to share meta-epidemiological study datasets with information on meta-analyses and trials included in meta-epidemiological studies. Here, we describe the COMFIT study, its database, and descriptive results. We included meta-epidemiological studies with published or unpublished data on trial funding source and results or conclusions. We searched five bibliographic databases and other sources. We invited authors of eligible meta-epidemiological studies to join the COMFIT consortium and to share data. The final construction of the COMFIT database involves checking data quality, identifying trial references, harmonising variable categories, and removing non-informative meta-analyses as well as correlated meta-analyses and trial results. We included data from 17 meta-epidemiological studies, covering 728 meta-analyses and 6841 trials. Seven studies (405 meta-analyses, 3272 trials) had not published analyses on the impact of commercial funding, but shared unpublished data on funding source. On this basis, we initiated the construction of a combined database. Once completed, the database will enable comprehensive analyses of the impact of commercial funding on trial results and conclusions with increased statistical power and a markedly reduced risk of confounding and reporting bias.