Well, let's be clear: It's getting smaller for younger women, say in the 20-34 range. Women under 35 who work full time earn around 90 percent of what the guys are making, according to a Labor Department report. But for those over 35 it's down to 75 percent. From Economix:
Older women may have entered the work force at a time when inequity in pay between the genders was more acceptable. Thus, even though more protections may exist today against outright pay discrimination, older women may have started from a lower salary base and, despite raises, will never catch up. The different mix of jobs that women versus men go into -- which helps explain a large part of the wage gap across the board -- may also have changed in recent decades. Unlike in the past, women today claim the majority of college diplomas awarded; perhaps that means that women today are going into higher-skilled (and higher-paying) jobs.
Women working full-time in the U.S. had median weekly earnings of $657 last year, or about 80 percent of the $819 median for men. In 1979, women earned about 62 percent as much as men. Within the states, the discrepancies are quite apparent: In California, median weekly earnings was $750 for women and $849 for men. In Louisiana, it was $518 for women and $797 for men.