Black male physicians earn substantially less than their white counterparts, while male doctors have higher incomes than females, according to a new study published in the BMJ.

Harvard Medical School PhD candidate Dan P. Ly authored the study along with Sean Seabury, PhD, associate professor at the University of Southern California, and Anupam Jena, MD, PhD, physician at Massachusetts General Hospital and a professor at Harvard Medical School.

The researchers used data from two separate sets of survey data: the American Community Survey (ACS), conducted by the U.S. Census Bureau and covering 2000 to 2013, and physician tracking surveys conducted by the Center for Studying Health System Change from 2000-01, 2004-05 and 2008. The ACS didn’t account for physician specialty, while the physician tracking data did, so the authors compared the two sets of data to find if any racial or gender disparity could be explained by choosing different specialties or type of practice.

The research found the pay gap persisted. The median annual pay for white male physicians ($253,000) was higher than black males ($188,000), while the difference between white and black females was smaller ($163,000 versus $153,000). When adjusting to account for specialties and practice characteristics, 35.4 percent of white male physicians had adjusted annual income above $250,000, compared to 27.1 percent of black males, 19.4 percent of white females and 18.9% of black females.

“Unfortunately, this means that medicine has not been spared the disparities by race and sex that plague the rest of the U.S. labor market,” Jena said in a statement.

The data used has limitations. The larger and more current ACS data doesn’t include information on specialty or practice characteristics, and it includes far more white physicians (43,000 men and 15,000 women) than black colleagues (1,600 men and 1,300 women). William Weeks, MD, PhD, senior research scientist at the Dartmouth Institute and professor at Dartmouth’s Geissler School of Medicine, said the study’s findings are more driven by the greater number of white specialists rather than by race.

“This is really not good research,” Weeks said to the Washington Post. "It's a poor design. It's a poor study. It should be ignored."

The study acknowledges the racial gap may be explained by black doctors choosing different specialties or treating more Medicaid patients. But it also suggested those factors may also be explained by discrimination.

“Importantly, even if subspecialty mediates some of the difference in income by race, such differences are still important to understand because differences in subspecialization might not only be because of preferences but also to unequal subspecialty opportunities for black physicians. That is, black physicians might have similar preferences for higher paying subspecialties but less opportunity to enter them,” Ly and coauthors wrote.

The study concluded more research is needed to determine whether job opportunity or other factors are to blame for the pay gaps.