A study conducted by a team of U.S. researchers found that financial ties between researchers and the companies that make the drugs they are studying are independently associated with positive trial results. The team’s work was published in The BMJ this week.

The study was observational, so the results can’t be used to draw concrete conclusions. But the authors write that since industry and academia collaborate to advance many 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.”

The researchers analyzed a random sample of 195 drug trials published in 2013, focusing on trials that examined the efficacy of drugs. More than half of the studies’ principal investigators had financial ties to industry, including travel expenses, honorariums or stock ownership.

Nearly 80% of positive studies were authored by principal investigators with financial ties with industry, compared to 49% among studies with negative results. The team also noted that authors from the U.S. were more likely to have financial ties with industry than authors from other countries.

Even accounting for factors like funding source and sample size, the results showed that trials authored by investigators with financial ties to drug manufacturers more likely to report favorable results than the authors without association to industry.

In light of their findings, the researchers conclude that trial authors should share their data and only participate in industry-funded trials if the data are made available to the public. Journals should reject authors who are unwilling to share their data, the team wrote, and trials with industry funding “should be interpreted with caution until all relevant information is fully disclosed and easily accessible.”