The study was published on Wednesday in the British Medical Journal and completed by researchers at several United States' universities.

It brings more light to the broader debate surrounding financial ties between the pharmaceutical industry and researchers conducting studies, doctors prescribing such drugs and patient advocacy groups lobbying for approval of new medicines.

While financial ties are common, concerns remain about the influence of industry on study design, methods, results and interpretations; and results from previous studies of such ties have been conflicting, triggering this latest research paper.

The study examined 195 clinical trials published in 2013 for any "association between the presence of individual principal investigators' financial ties to the manufacturer of the study drug" and the trial's outcomes, after accounting for the sources of research funding.

It focused on drug trials that centred on "efficacy", or the effectiveness of a particular drug, as such trials had a larger impact on clinical practice and healthcare costs.

The research found 67.7 per cent (132) of those clinical trials examined had financial ties between the principal investigators on the trial and the wider pharmaceutical industry.

Of 397 "principal investigators" on the trials studied, 231 or 58 per cent had direct financial ties to the industry while 166, or 42 per cent, did not.

Among those with financial links, the most common type was: advisory or consultancy payments in 39 per cent of cases; "speakers' fees" in 20 per cent of cases; "unspecified financial ties" in 20 per cent and "honorariums" in 13 per cent.

The study found some 76 per cent of principal investigators on the clinical trials studied that reported "positive" findings, had financial ties of some description to the industry or pharmaceutical company funding the trial.

In those studies that found "negative" results, some 49 per cent of principal investigators were found to have financial ties to the industry.

"Financial ties of principal investigators were independently associated with positive clinical trial results," the paper reads.

While the study results did not necessarily suggest a "causative" relationship between positive trial outcomes and financial links, it did report the findings "may be suggestive of bias in the evidence base".

The authors pointed to potential links between industry funding, financial ties and trial results including: bias in "selective outcome reporting", lack of publication of negative results and "inappropriate analyses".

Study authors also urged that "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", given the growing collaboration between medical research institutions and the corporate world.

University of Sydney researcher Lisa Bero and University of Southern Denmark's Andreas Lundh said more research was needed to identify the influence of such ties on trial results.

Both academics urged that researchers only participate in industry-funded trials if data were released publicly, financial ties were disclosed and sponsors were transparent.

But, until such measures were mandated, Professors Bero and Lundh urged that trials with such financial ties with authors be "interpreted with caution until all relevant information is fully disclosed and easily accessible".