DOES MARRIAGE MATTER? The sociologists with The National Marriage Project at the University of Virginia think so. Their latest reports offers some good--and not so good--news.

On the upside, divorce is down. In fact, it's plummeting to levels not seen since before the 1970s "divorce revolution" made splitting up easier (legally and socially) than ever. About 23 percent of couples who married in the early 1960s divorced before their first child turned 10; today, just a bit more than 23 percent of couples who married in the mid-1990s have divorced.

On the other hand, one reason divorce has diminished is that its shadowy twin, cohabitation, is on the rise, and with it, family instability. The study found that nearly a quarter of children today are born to cohabiting couples, and another 20 percent will be exposed to that lifestyle during their childhood.

So what's the big deal, some would ask. Isn't marriage just a piece of paper, anyway?

In fact, says the study, "[c]hildren are less likely to thrive in cohabiting households, compared to intact, married families." They score worse on measures of social, educational, and psychological outcomes, and, according to federal data, are more likely to suffer from abuse.

Family instability in general is bad for kids. "Transitions" that occur when parental partners move in and out of the home "are linked to higher reports of school failure, behavioral problems, drug use, and loneliness, among other outcomes" for kids.

Furthermore, instability is increasing as Americans step "on and off the carousel of intimate relationships" with increasing rapidity, the study says, quoting sociologist Andrew Cherlin. Sadly, the prevalence of cohabitation is higher among lower- and middle-income Americans. Marriage--and therefore family stability--is actually gaining strength in the college-educated and affluent realms of American society.

The study concludes that "[t]he intact, biological, married family remains the gold standard for family life in the United States, insofar as children are most likely to thrive--economically, socially, and psychologically--in this family form." Furthermore, "[m]arriage is an important public good."

Which is not to say every married couple ought to stay that way, especially if there's abuse involved. Still, public policy that supports marriage, and frowns on cohabitation, is good medicine. You can read more at virginia.edu/marriageproject.