To assess the association between competing interests and authors' conclusions in randomised clinical trials.
Epidemiological study of randomised clinical trials published in the BMJ from January 1997 to June 2001. Financial competing interests were defined as funding by for profit organisations and other competing interests as personal, academic, or political.
159 trials from 12 medical specialties.
Main outcome measures
Authors' conclusions defined as interpretation of extent to which overall results favoured experimental intervention. Conclusions appraised on 6 point scale; higher scores favour experimental intervention.
Authors' conclusions were significantly more positive towards the experimental intervention in trials funded by for profit organisations alone compared with trials without competing interests (mean difference 0.48 (SE 0.13), P=0.014), trials funded by both for profit and non-profit organisations (0.30 (SE 0.10), P=0.003), and trials with other competing interests (0.45 (SE 0.13), P=0.006). Other competing interests and funding from both for profit and non-profit organisations were not significantly associated with authors' conclusions. The association between financial competing interests and authors' conclusions was not explained by methodological quality, statistical power, type of experimental intervention (pharmacological or non-pharmacological), type of control intervention (for example, placebo or active drug), or medical specialty.
Authors' conclusions in randomised clinical trials significantly favoured experimental interventions if financial competing interests were declared. Other competing interests were not significantly associated with authors' conclusions.
What is already known on this topic
Financial competing interests may influence authors' conclusions—for instance, interpretation of whether results favour the experimental or control intervention
Trials of antipsychotic drugs for schizophrenia funded by drug companies were more likely to show a benefit of treatment
It is not known whether other competing interests, such as personal, academic, or political, are associated with authors' conclusions.
What this study adds
In pharmacological and non-pharmacological randomised clinical trials from 12 specialties financial competing interests were significantly associated with authors' conclusions
The association did not reflect inadequate methodological quality, greater statistical power, or use of inactive control interventions
Personal, academic, and political competing interests were not significantly associated with authors' conclusions.