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As fewer couples marry, some argue the institution really isn't crucial; kids just need two parents committed to raising them. Others argue that marriage provides stability that's otherwise elusive and provides the best likelihood kids will thrive.

Marriage is becoming a hot topic among sociologists, who debate if social policy should be encouraging the institution of marriage or focusing on bolstering relationship traits that seem to go along with marriage.

It's the chicken-and-the-egg question of family structure: Is it marriage that increases the stability and resources that allow kids to thrive? Or is it simply that people who have traits that benefit children are the most likely to marry?

The issue is posed by a new Brookings Institution report from Kimberly Howard and Richard V. Reeves: "But it is important to try and understand why the children of married parents do better. Is it simply because they have, on average, higher family incomes? (Two earners are better than one, and one household is cheaper to run than two.) Or are two committed spouses better able to provide consistent parenting? Is it marriage itself that matters, or is marriage the visible expression of other factors, that are the true cause of different outcomes? And if so, which ones?"

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They note that parents who stay married have more time, education and income to bring to the task of raising children than do single moms or dads "and it may be these differences that lie behind the gaps in their children’s success, rather than the fact of marriage itself." They say two factors — more money and more engaged parenting — are responsible for the benefits enjoyed by children who are raised by their married parents.

If you could provide kids with those benefits outside of a married-parent family, the advantage of marriage would likely disappear from kids' lives, they said. "Perhaps it's not that children are better off when their parents marry — it's that the qualities that enable successful marriages also make good parents."

W. Bradford Wilcox, director of the National Marriage Project at the University of Virginia, believes the beneficial outcomes associated with marriage do actually result from marriage.

In a blog for the Institute for Family Studies, he wrote, "The new progressive line on marriage fails to appreciate three truths about contemporary family life and public policy. 1) Marriage itself generates more money and is conducive to better parenting, on average, than the alternatives. It’s also much more stable for children. 2) The federal government has neither the will nor the ability to erase the income and parenting deficits associated with single parenthood. 3) The deficits associated with single parenthood can be found even in countries, like Sweden, that have more generous welfare policies than does the United States."

He backed his findings regarding Sweden with a report from the U.S government's National Center for Biotechnology Information.

"No other institution reliably connects two parents, and their money, talent, and time, to their children in the way that marriage does," Wilcox said. "And given that we cannot count on the federal government to launch a Swedish-style public policy push to bridge the economic and parenting divides between children raised inside an intact, married family versus outside of one, the question then becomes: Can anything be done to increase the odds that every American child has an equal opportunity to be raised by his or her own parents in a strong and stable marriage?"

These questions should matter to policymakers since efforts to promote marriage have not been hugely successful. Sixty years ago, more than 90 percent of children under 15 were raised by their married parents; the number is now less than two-thirds, according to a recent report for the Council on Contemporary Families by University of Maryland sociology professor Philip Cohen. He said odds are only about even that two randomly selected children have the same living situation.

Emily Badger, who writes the Washington Post Wonkblog, explained the choices before policy makers to address the problem: "If we believe that marriage itself is what matters for children, then we'd want to encourage parents to marry. If we believe it's the financial stability that matters, then we'd want to find ways to bolster the income of single parents outside of marriage. If we believe it's the good parenting skills so often present in married households that make the difference, we could try to instill those skills in parents regardless of whether they have spouses."

Some experts believe another solution is to help single parents follow a pattern common among the higher income, college-educated American couples who are far more apt to be married when they have children: Be deliberate in the decision to have children and don't have unplanned pregnancies for which you're not ready.

"Not only are 40 percent of all children born outside marriage (50 percent among mothers under 30), but 60 percent of these births were unplanned," said Brookings senior fellow Isabel V. Sawhill in a recent New York Times opinion piece. Better family planning tools like modern contraceptives help that process, she said, as long as individuals can access them.

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