Even in nursing, where women make up an overwhelming majority of the profession, female nurses are paid less than their male counterparts. According to new research from the Journal of the American Medical Association (JAMA), male registered nurses (RNs) on average make nearly $11,000 more per year than female RNs. The kicker: only half of this gap can be explained by variables such as education, specialty, and work experience. That leaves a $5,148 gap in salary between male and female nurses -- essentially a gender-based salary gap, which according to researchers affects 2.5 million women and their families.

The study was conducted by Ulrike Muench, a nurse practitioner and Yale Ph.D., who is currently studying at University of California, San Francisco, and her colleagues at Yale and Vanderbilt University. The researchers analyzed data from two different surveys. In one, they looked at two decades worth of data from the National Sample Survey of Registered Nurses, which ended in 2008. For the second, the researchers examined the salaries of registered nurses who took part in the U.S. Census Bureau’s American Community Survey from years 2001 to 2013.

The National Sample Survey of Registered Nurses collected data from RNs once every four years and overall contained data from 87,903 full time registered nurses. Of the respondents, only seven percent were men (93 percent were women).

Before accounting for factors such as hours worked per week, number of years of experience, location and type of degree held, the raw data found that male nurses made on average $10,775 more per annum than women. Even after the effects of those factors were excluded, male RNs still made $5,148 more than female RNs.

Just as striking, the research found that the pay gap existed to varying degrees every year since 1988. Graphs, which can be found here, show that wages nearly caught up in the late 1990s, but spread out again in the 2000s.

From the U.S. Census' American Community Survey, researchers looked at over 200,000 RN salaries. Through that data, researchers found that the 10 percent of male respondents earned on average $9,562 more than their female counterparts, prior to adjusting the numbers to account for hours, location, degree and experience. Again, the visual data from this survey shows a startlingly persistent gap between male and female wages.

The pay gap in female-dominated nursing is not unique. There is also a pay gap in female-dominated public relations.

ATTN: put together a video explaining how the pay gap affects millions of women across the country: