The gender gap between men's and women's pay and employment -- which some analysts attribute to discrimination and others to different life choices -- is disappearing.

Today, women make up almost half of the U.S. workforce.

• Since 1960, the proportion of single women in the workforce has jumped from 58.6 percent to 66.4 percent.

• The proportion of married women who work has climbed from 31.9 percent to 59.4 percent in that time.

• They hold two out of every five management jobs -- compared to just 14 percent in 1960.

Yet only 7 to 9 percent of senior managers in Fortune 1000 companies are women. Nevertheless, that's a huge increase from just 1.5 percent in the mid-1980s.

Real progress has been made in the number of women owning their own firms.

• They own some 7.7 million firms -- up 43 percent since 1990.

• Their firms had a total $1.4 trillion in sales last year.

• These firms employ some 15.5 million people in the U.S. alone -- 35 percent more workers than in Fortune 500 companies.

Demographers think one reason for these advances is more education. Over the past 35 years, more and more women have earned higher degrees. In 1960, less than 4 percent of master's degrees in business went to women. Today, more than one-third do.

Source: Charles Oliver, "Is the U.S. Gender Gap Shrinking?" Investor's Business Daily, February 22, 1966.