When the European Union commissioner Viviane Reding called for a quota system last week so that more women would get into boardrooms, she raised predictable protests. Even Reding, the senior justice official for the EU, admitted that she wasn't a fan of quotas.



"However,'' she said, "I like the results they bring."



But what if her real mistake was that she asked for the wrong quota?



In the U.S. women occupy fewer than 15% of the seats on corporate boards, and only 2.6% of chief executive offices of Fortune 500 companies. In Europe, the numbers are even worse, prompting Reding's exasperation. But for women to really get ahead in the boardroom, we need a quota on how much time men spend helping out at home.



Women already have what it takes to make to the corner office on their own. Females are competitive with males in academic programs when they are given the chance to compete. And according to a 2007 McKinsey and Co study of 89 European companies, firms with more female leadership had a better return on equity, growth in stock prices and operating results than firms dominated by men.



Correlation is not causality. Perhaps there were other reasons those firms with women were profitable. But in a globally competitive market, there is no reason to think that passing over talent in a skirt is a winning strategy or that it's a good idea to forgo insights from leaders likely to have better insights into consumer demand for half of the world's population. You might think that firms should be rushing to hire more women.



Why not? Fewer women than men have the "round the clock availability" that it takes to be a corporate leader. The problem is that, in today's world, women do more family work than men -- a lot more. The U.S. Bureau of Labor Statistics, which tracks how much time people spend in various activities, reports that in 2010 American families with children under the age of six did not share family work equally. Women spent an average of 1.1 hours a day with children while men spent an average of 26 minutes.



Employers know that women are more likely than men to drop out or reduce their hours during child-bearing years -- precisely the time in a person's life when many men put on the steam to achieve career success. But the problem is not only during the child-bearing years. The Bureau of Labor Statistics reports than on an average day in 2010, "20 percent of men did housework -- such as cleaning or doing laundry -- compared with 49 percent of women. Forty-one percent of men did food preparation or cleanup, compared with 68 percent of women." Then there are aging parents to take care of, and the list goes on.



A 2009 survey of faculty at Berkeley found that men and women do not spend equal time on family work until age 62. To the extent that productivity is related to hours worked, the ability to put long hours in the office and to forgo work interruptions on account of family responsibilities are important factors in career success.



The bottom line is that the plum jobs and the fattest paychecks go to the people who have the hours to spend in the office.



What should we do about it? Mandating paternity leave and family work would fix the problem but it would not work in practice. Even if such a scheme were to pass muster with the U.S. Supreme Court, ambitious men could refuse to claim paternity rather than to help with the kids -- an option not available to mothers. In Sweden, where men are bribed to take parental leave with a take it or leave it "daddy month," many men choose to continue working, signaling their willingness to "do what it takes" to get to the top. MIT has found that male faculty granted parental leave are more likely than female faculty to spend the time working on their scholarship and attending conferences rather than staying home with the baby.



Better and cheaper childcare would help more women enter and stay in the workforce. But we know from Scandinavia, where universal childcare is available, that helping women get and hold jobs does not help them climb all the way to the top of the corporate ladder. Even in Sweden, where government support for childcare is among the most generous in the world, few women make it into the top corporate jobs, and among those who do, disproportionately few (60% compared to 95% for men) are married with children.



So what can we do? Help poor women afford good childcare so they can earn an income and so their children can become strong contributors to society. Organize the workplace so people don't need to work continuous hours to remain productive. Find better ways to measure productivity than hours logged. But most importantly, raise children who will grow up thinking that family work is not a woman's job. Unless and until men are willing to spend as much time at home as women, the boardroom will be a man's world.