The Stanford Center for the Study of Poverty and Inequality has collected 20 facts about inequality in the United States that “everyone should know.”
The fifth one, illustrated above, refers to gender pay gaps (measured in terms of women’s earnings as a percent of men’s, for full-time wage and salary workers, annual averages):
Throughout much of the 20th century, the average woman earned about 60% of what the average man earned. Starting in the late 1970s, there was a substantial increase in women’s relative earnings, with women coming to earn about 80% of what men earned. This historic rise plateaued in 2005 and, since then, the pay gap has remained roughly unchanged.