NEW YORK: US female doctor-researchers make an average of $12,000 a year less than their male counterparts, even after their work hours and area of specialty are taken into account, according to a study released on Tuesday.

Doctor-researchers have both medical degrees and PhDs, and they see patients as well as conduct medical studies.

The wage gap between men and women is nothing new, but among doctors in particular it wasn't clear if the disparity was due to different career choices and work habits in men and women that could have affected their pay.

“Disturbingly, even after we controlled for all those other factors, we found that male doctors were paid more than female doctors for doing the same work,” said Dr Reshma Jagsi, the lead author of the new study from the University of Michigan in Ann Arbor.

The findings were published in the Journal of the American Medical Association.

Jagsi and her colleagues sent questionnaires to 800 doctor-researchers in the United States, all of whom had previously won a mid-career grant award from the government.

The doctors were an average of 45 years old at the time of the survey and three-quarters of them were white.

Men reported making an average of slightly over $200,000 per year and women about $168,000.

The researchers found women were more likely to work in lower-paying specialties such as pediatrics and family medicine.

Female doctors also tended to work slightly fewer hours than their male peers – 58 hours per week on average, versus 63 for men.

Those differences were responsible for some of the salary gap. But even after Jagsi's team accounted for income disparities that could have been due to career and life choices, the researchers found women still made about $12,000 less than men doing the same type and amount of work.

Conscious Trade-Offs or Bias?

That's similar to what has been found in past research, such as in studies of early-career doctors, according to Anthony Lo Sasso, a health policy and economics researcher from the University of Illinois at Chicago.

But the finding still leaves many unanswered questions, said Lo Sasso, who wasn't involved in the new research.

“It really doesn't get at what the underlying driver is, and I think that remains the puzzle at this point – what is accounting for this unexplained salary difference?”

One explanation, according to the researchers, is that women are less aggressive about negotiating for pay or may take factors other than salary, such as location and community, into account when choosing a job.

Lo Sasso said it's possible women in the study accepted slightly lower pay in return for less time being on-call and more predictability in their schedules. Those types of questions were not included in the survey.

The researchers calculated that over her career, the average female doctor-researcher would make about $350,000 less than a man doing similar work because of unexplained salary differences.

Jagsi said she worries the findings may hint at unconscious biases in hiring and pay at the academic institutions where these researchers worked. One way to address that, she said, is for employers to have clear policies about how salaries are determined so doctors can know if they're being paid fairly.

That applies outside of hospitals and universities as well, she said. A report released in April showed American women make 77 cents for every dollar earned by men, a gap that is even bigger in certain professions, such as financial management.