Female doctors earn an average of $56,000 less each year than male doctors, according to a new study, which found that gap hasn't budged since the late 1980s.

Researchers found that although earning gaps shrank over time among non-healthcare workers, that was not the case for doctors and certain other health professionals.

"There is something that's intrinsically going on within the physician workforce," said Dr. Anupam B. Jena, the study's senior author from Harvard Medical School's Department of Health Care Policy.

Taking into account hours worked and years of experience - but not specialty - they found the average male doctor earned about $221,000 in 2006 to 2010, and the average female doctor earned $165,000.

Income gaps held steady at about a 40 percent difference in pay among male and female dentists. Disparities fell slightly over time to about 11 percent for pharmacists and 6 percent for registered nurses, the researchers reported in JAMA Internal Medicine.

During the same time period, they found salary differences between men and women outside of healthcare dropped from 28 percent between 1987 and 1990 to 15 percent between 2006 and 2010.

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