While the gender wage gap appears to be disappearing in the general work force, the exact opposite is happening in the health care sector: New research in the Journal of the American Medical Association suggests that the gender pay gap among doctors, dentists and other health care workers has grown over the past decade.

In the late 1980s, male physicians earned $33,840, or 20 percent, more in annual salary than their female counterparts. By the late 2000s, that grew to a 25.3 percent gap, a difference of $56,019 per year. The same trends showed up among dentists and physician assistants, but not pharmacists or health insurance executives.

The study adjusted for hours to avoid overstating gender differences, such as if female doctors worked fewer hours, and also accounted for years of experience.

One factor researchers were not able to adjust for though was specialty, which is important: Specialists, such as surgeons or radiologists, tend to earn significantly more than primary care providers. Women account for more than half of the country's pediatricians but fewer than 10 percent of orthopedic surgeons, according to data from the Association of American Medical Colleges.

Authors Seth Seabury, Amitabh Chandra and Anupam Jena write that, even without the specialty adjustment, the space between male and female doctors' salaries still merits examination.

"This is because speciality and practice choice may be due not only to preferences of female physicians but also unequal opportunities," they contend. "For example, are unadjusted earnings differences between male and female physicians due to a preference of female physicians for lower-paying specialties (eg, pediatrics or primary care), or do female physicians have less opportunity to enter higher paying specialties despite having similar preferences as male physicians?"