There are many feel-good, fairness-based reasons to hire and invest in women. You're probably familiar with at least a few of them: Women have historically had fewer opportunities in the workplace. They don't get promoted as frequently. They are increasingly the sole or primary breadwinner for their families. Also, women's lib and girl power and something about Half the Sky.

There's an even better reason that is less frequently cited. Women, you see, will make you money.

A new report from the California-based Anita Borg Institute makes the case that profitability, rather than charity or good PR, should convince companies to try harder to cultivate female talent on the payroll and in the C-suite.

Several studies have found, for example, that companies with a greater representation of women on their boards or top management teams tend to perform better. It's not clear what's cause and what's effect here. Research suggests, though, that diversity of any kind -- related to gender, race or other demographics -- is good for problem-solving and idea generation.

One lab experiment, for example, found little correlation between a team's collective intelligence (measured by performance on group tests such as visual puzzles) and the IQs of the team's individual members. But it did find that having a higher share of women on the team raised collective intelligence.

It's not just in corporate settings that estrogen seems good for business. In an analysis of Hollywood films for FiveThirtyEight.com, Walt Hickey recently argued that "films that feature meaningful interactions between women may in fact have a better return on investment, overall, than films that don't." That may be related to the fact that women represent a major customer base as well as employee pool.

And perhaps the best argument for why hiring women will help your firm's bottom line: They still, amazingly, come at a discount. At least for now.

Tuesday is Equal Pay Day, the symbolic reminder of how far into 2014 women would have to work to catch up to the wages earned by men last year, thanks to the intransigent gender pay gap. Some of the gap is explained by the types of occupations women go into, either by choice or opportunity. But even within occupations, women almost always earn less than their male counterparts. Of all the occupations the Bureau of Labor Statistics published data for last year, only three showed women receiving higher median weekly earnings than their male counterparts: bakers; wholesale and retail buyers; and miscellaneous computer-related occupations. Even controlling for factors such as experience, industry and union status still leaves about 40 percent of the total gender pay gap unexplained.

Whether women earn less than men because of discrimination (deliberate or unconscious) or other factors is debatable. Many have attributed the pay differential to the fact that women don't negotiate as aggressively over their compensation as men do. Women expect to be automatically rewarded for their good work, the story goes, whereas fist-pounding men burst into the boss' office and demand the raise they know is rightfully theirs.

Whatever the reason, the fact that women's pay is lower does mean they're a better deal for employers.

Smart employers will recognize a bargain when they see it and scoop up the undervalued talent. Way back in 1983, Alan Greenspan explained this in an interview about his own hiring preferences: "I always valued men and women equally, and I found that because others did not, good women economists were cheaper than men. Hiring women does two things: It gives us better-quality work for less money, and it raises the market value of women.''

Perhaps these arguments sound beside the point; few are really arguing against hiring women these days. Indeed, law firms, Wall Street banks, tech companies and other big, male-dominated businesses have all sorts of outreach programs to identify and nurture female talent (especially, it seems, when the stuff is about to hit the fan: witness the unfortunate timing of Mary Barra's coronation at General Motors). And yet female representation across these industries and occupations -- especially in management positions -- is alarmingly low.

That's because lip service isn't enough. Corporate policy matters, too. As long as firms are resistant to changes that will help attract and retain female talent -- like more flexible work arrangements, which can actually boost worker productivity -- they will be limiting their own potential as well as that of female workers.

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Rampell, a former economics reporter for The New York Times, writes a twice-weekly column for The Washington Post.