A study published this month in BMJ offers additional evidence of a correlation between payments by drug manufacturers to doctors and increased prescriptions for drugs developed by the latter.

The analysis of Medicare’s Open Payments program offers a statistical demonstration of a phenomenon supported by more than 20 years of suggestive data, though the study’s authors point out that most previous studies have relied upon self-reporting to obtain payment and prescribing data. Where a recent study published in JAMA established a link between the free meals pharmaceutical companies offer and increased prescriptions, this new study expands that purview to include payments for speaking and consulting fees, as well as indirect payments for education, or for food and entertainment.

Moreover, the authors see a potential connection between payments made to physicians and “substantial differences in regional prescribing.” They conclude that “one additional payment in a region [median value $13] was associated with approximately 80 additional days filled of the marketed drug in the region.” As damning as that sounds, the authors caution that their study doesn’t prove the payments actually led to the increased prescribing, and say that their findings should not be interpreted beyond a regional level.

Even absent clear evidence of causation, pharmaceutical companies continue to make payments to doctors, most of whom don’t believe they can be influenced, according to the study.

Reporting by ProPublica undermines this claim, showing the industry’s efforts seem to specifically target physicians already under sanction for unnecessary prescribing. The preponderance of the evidence suggests pharmaceutical companies have a profit motive behind their actions, according to Charles Rosen, co-founder of the Association for Medical Ethics, who told ProPublica, “I think it’s crystal clear that their fiduciary duty is not to educate physicians and make public welfare better. It’s to sell a product.”

Pharmaceutical and medical device companies are continuing to pay doctors as promotional speakers and expert advisers even after they’ve been disciplined for serious misconduct, according to an analysis by ProPublica.

One such company is medical device maker Stryker Corp.

In June 2015, New York’s Board for Professional Medical Conduct accused orthopedic surgeon Alexios Apazidis of improperly prescribing pain medications to 28 of his patients. The board fined him $50,000 and placed him on three years’ probation, requiring that a monitor keep an eye on his practice.

Despite this, Stryker paid Apazidis more than $14,000 in consulting fees, plus travel expenses, in the last half of 2015.

Stryker also paid another orthopedic surgeon, Mohammad Diab of San Francisco, more than $16,000 for consulting and travel, even though California’s medical board had disciplined him for having a two-year-long inappropriate sexual relationship with a patient, whose two children he also treated. He was suspended from practice for 60 days, required to seek psychological treatment and given seven years’ probation. He is still required to have a third party present while seeing female patients.

According to the ProPublica investigation Stryker is one of more than at least 400 pharmaceutical and medical device makers that have made payments to doctors after they were disciplined by their state medical boards. ProPublica reviewed disciplinary records for doctors in five states, California, Texas, New York, Florida and New Jersey, and checked them against data released by the Centers for Medicare and Medicaid Services on company payments to doctors. The analysis identified at least 2,300 doctors who received industry payments between August 2013 and December 2015 despite histories of misconduct.