Financial ties between researchers and companies that make the drugs they are studying are independently associated with positive trial results, suggesting bias in the evidence base, claims a study published by The BMJ.
Relationships with industry are common among investigators of randomised clinical trials (RCTs) - raising concerns about the effect that financial ties may have on the evidence base. But studies investigating these relationships have been conflicting.
So a team of US based researchers set out to investigate the association between financial ties of principal investigators and study outcomes in a random sample of 195 drug trials published in 2013.
More than half (58%) of principal investigators had financial ties to the drug industry - including travel expenses, honorariums, payment for advisory work, or stock ownership.
The results show that trials authored by principal investigators with financial ties to drug manufacturers were more likely than other trials to report favourable results.
Even after accounting for factors that may have affected the results, such as funding source and sample size, financial ties were still significantly associated with positive study outcomes.
The authors point to possible mechanisms linking industry funding, financial ties, and trial results such as bias by selective outcome reporting, lack of publication, and inappropriate analyses.
They stress that their analysis is observational and cannot be used to draw conclusions about causation, but say, given the importance of industry and academic collaboration in advancing the development of new treatments, "more thought needs to be given to the roles that investigators, policy makers, and journal editors can play in ensuring the credibility of the evidence base."
More research is certainly needed to identify how industry funding and financial ties could influence trial results, say Andreas Lundh from the University of Southern Denmark and Lisa Bero from the University of Sydney in a linked editorial.
They urge trial authors to share their data and participate in industry funded trials only if data are made publicly available - and suggest journals could help by rejecting research by authors who are unwilling to share their data and by penalising authors who fail to disclose financial ties. The role of sponsors, or companies with which authors have ties, in the research must also be transparent.
In the meantime, trials with industry funding or authors with financial ties "should be interpreted with caution until all relevant information is fully disclosed and easily accessible," they conclude.