Background: Evidence suggests that published industry-sponsored drug trials are more likely to report results and conclusions that favour the drug over placebo. Less is known about potential biases in drug-drug comparisons.

Objectives: To examine associations between research funding source, study design characteristics aimed at reducing bias, and other factors with results and conclusions published in randomized controlled trials (RCTs) of drug-drug comparisons.

Methods: Cross-sectional study of 192 published RCTs evaluating the efficacy of a statin drug compared to another statin or alternative drug class for the treatment and prevention of cardiovascular disease. Data on concealment of allocation, selection bias, blinding, sample size, disclosed funding source, financial ties of authors, results for primary and secondary outcomes, and author conclusions were extracted by two coders. Inter-coder reliability was very good (weighted kappa .80-.97).

Results: Half of the RCTs (95/192) were funded by industry and 37% (70/192) did not disclose any funding source. In the full sample, industry funding was not associated with results, but was associated with conclusions that favoured the sponsor (p=.017). For the subset of RCTs that were industry funded (n=95), results and conclusions favoured the sponsor's product, rather than the comparison drug (Table). In multivariate analysis, results (OR 9.2; 95%CI 3.5-24.4) and conclusions (OR 8.0; 95%% 3.2-19.9) favoured the sponsor's product after controlling for other study design features.

Conclusions: RCTs of statin drug-drug comparisons are more likely to report results and conclusions favouring the sponsor's product compared to the comparison drug. This bias in drug-drug comparison trials should be considered when making health policy decisions regarding drug choice, such as drug formulary decisions.