Women make 78 cents for every dollar made by men. But the wage gap isn't that simple.

The stat we're all so familiar with "is an aggregate of all men and women in the workplace," said Christina Hoff Sommers, a resident scholar at the American Enterprise Institute. It doesn't take into account important variables like education level, total hours worked, type of work and job tenure, she said.

So, while Census Bureau data says the average woman working full time made nearly 22% less than her male counterpart in 2013, or 78.3 cents on every dollar, that doesn't mean that all women get paid less to do the exact same job as men.

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But there is research that does indicate a discrepancy.

A study from the American Association of University Women that controlled for college major, occupation, age, geographical region, hours worked and more, showed there is still a 7% wage gap between male and female college grads a year after graduation.

"We reviewed men and women who have made exactly the same education and career choices and still found a gap," said Lisa Maatz, vice president of government relations at the AAUW.

The trend is particularly troublesome given that mothers are the primary breadwinners in 40% of U.S. households with children, according to a 2013 Pew Research Center report.

Some blame the pay gap on womens' career choices and family demands. Others fault workplace discrimination, or women's reluctance to negotiate for pay and promotions.

To make pay more equal, Maatz said society needs to add more value to "pink-collar jobs" that tend to be low-paying.

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"We want women to go into lucrative professions, but we still need child-care workers, teachers and secretaries," she says. "These jobs are needed, but aren't valued as much monetarily and that needs to change."

The 78 cent wage gap is an improvement, according to the Census Bureau, up from 76.5 cents in 2012.

But the increase could have more to do with the decline of men in the labor force than gain for women.

"Men ages 25-34 have seen their wages fall 20% since 1980," said Kim Parker, director of social trends research at the Pew Research Center. "So while there's been some wage improvement for women, the fall for men has been more significant [on closing the gap]."

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Another Pew researcher, Rakesh Kochhar, points out that the wage gap gets smaller every time a new generation enters the workforce, but then climbs back up to about 75% by mid-career.

"We have no smoking gun on why that happens," Kochhar said, "except that it coincides with the age when most women take time off for motherhood and other family matters."