Background There is disagreement but few objective data on the relative quality of publicly or privately funded research. Cochrane reviews of randomized trials provide a good comparison opportunity because there is widespread agreement on how trial quality should be assessed and the Cochrane reviewers routinely do this.
Aims To compare the quality of publicly or privately funded randomized controlled trials.
Methods A total of 105 trials included in two Cochrane reviews were studied. Their quality assessments were abstracted from the relevant review and information about their funding source was collected from the original trial publications.
Main results Funding information was obtained for 87 trials. Of these, trials funded by pharmaceutical companies were larger (median sample size 126 vs. 45, P < 0.001), more likely to have avoided ascertainment bias 11/14 vs. 15/41 (P = 0.05). Non-significant trends in avoiding entry bias 19/19 vs. 35/37 and performance bias 13/22 vs. 14/48 also favoured the commercial trials. Commercial trials also had higher recorded attrition rates (median 6% vs. 1%, P = 0.007), but this difference was entirely caused by more non-commercial trials reporting a zero attrition rate.
Discussion The apparently lower attrition rate in the non-commercial trials should be interpreted with caution. Zero attrition in clinical trials with follow-up of many months is somewhat implausible.
Main conclusion Commercially funded randomized trials tend to be of higher methodological quality than government-funded ones.