Male nurses in the United States have earned thousands of dollars more than female nurses every year for nearly the past three decades, if not longer, and there's no sign of the gap getting any smaller, a new study has found. The results show that male registered nurses, on average, are earning over $5,100 more each year than female registered nurses. The salary gap was present across all nursing specialties aside from orthopedics, ranging from a low of $3,792 for chronic care to a high of $6,034 for cardiology.

The researchers determined the wage gap by looking at data from the National Sample Survey of Registered Nurses, which was taken every four years from 1988 to 2008. They also used data from American Community Survey between 2001 and 2013. While the surveys provided them with a large sample of close to 300,000 responses, the data is all self-reported. The study, which was conducted in part by the University of California, San Francisco, was published today in The Journal of the American Medical Association.

A huge pay gap remains in the US, with women earning, on average, 78 cents for every dollar that a man earns, according to the US Census Bureau. The statistics for registered nurses are particularly startling because, as the study points out, the field is dominated by women: in 2013, the US Census Bureau counted 3.5 million nurses, of which 3.2 million were women and 330,000 were men (only 78 percent of nurses were registered nurses). Despite that, the minority of men in the field — about one for every ten women — are still paid more.

The pay gap has been closing in the US, albeit very slowly. According to The New York Times, the national pay gap is at a record low, but the US still hasn't closed even half of the gap present in 1960, when women earned 60 cents for every dollar a man earned.

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