A new study by the Boulder, Colorado-based National Center for Women and Information Technology finds that women are leaving computer careers in staggering numbers.

"Fifty-six percent of women in technology companies leave their organizations at the mid-level point, 10-20 years in their careers," says Catherine Ashcraft, the senior research scientist who authored the report.

In 2008, women held only 25 percent of all professional IT-related jobs, down from 36 percent in 1991, according to the group's report, "Women in IT: The Facts."

Women's Pay Still Lags

Ashcraft says that women's pay, after 15 years, is 11 percent less than men with comparable experience.

In 2008, women in technology made an average salary of $70,370; men's pay during the same time period was $80,357.

The report shows that about half the women who leave science, engineering and tech jobs continue to use their technology skills, either starting their own companies or finding positions in government or nonprofits.

The others, however, say goodbye to their extensive training, taking non-tech jobs or leaving the work force completely.

Why Women Are Leaving IT

Ashcraft says that women are discouraged and leave for a wide range of blatant and subtle reasons. "Unconscious bias and gender pay gaps are significant factors," she says.

"Other factors that women point to for leaving the IT workforce include isolation, lack of role models and mentors, poor supervisory relationships and competing life responsibilities."

"If these trends continue, by 2018 the U.S. tech industry will only be able to fill half the available IT jobs," says Ashcraft.