An interesting study:

Put a man and a woman side by side at the same firm, with the same background, job title and productivity level, and you might be surprised when you look at their paychecks.

Though an often-cited statistic says women take home 76 cents for every dollar a man does, men and women who work side by side typically earn the same, researchers say.
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New research appears to knock down any lingering suspicions that employers blatantly discriminate against women in their pay. It instead attributes the gender gap in pay to more basic cultural realities, such as the fact that women are far more likely than men to step back from their careers to care for children. They quit their jobs for a time, or take lower-paying jobs that offer "flex time" or choose lower-paying careers with child-friendly hours, such as teaching.

On average, women who work the same hours as men make less in nearly every occupation, federal Department of Labor statistics for 2001 show.

"The wage gap--after accounting for legitimate differences that reflect choices and not discrimination--is really very small," said June O'Neill, a professor of economics in the business school at Baruch College in New York and a former director of the Congressional Budget Office.

A study by O'Neill in this month's American Economic Review explains up to 97 percent of the wage gap in salaries for men and women 35 and 43 years old as being a matter of choices made, not discrimination suffered.

The biggest factor, O'Neill found, is the number of years worked since age 18. She also found that women who wait until after 30 to have a child earn 7 percent more, on average, than those who don't.