Divorce is on the decline in the USA, but a report to be released today suggests that may be due more to an increase in people living together than to more lasting marriages.

Janna Cordeiro and Sebastian Toomey, both 30, have been together for over 10 years and have no plans to get married. The couple lives in Atlanta.

By Michael Schwarz, USA TODAY

Couples who once might have wed and then divorced now are not marrying at all, according to The State of our Unions 2005. The annual report, which analyzes Census and other data, is issued by the National Marriage Project at New Jersey's Rutgers University.

The U.S. divorce rate is 17.7 per 1,000 married women, down from 22.6 in 1980. The marriage rate is also on a steady decline: a 50% drop since 1970 from 76.5 per 1,000 unmarried women to 39.9, says the report, whose calculations are based on an internationally used measurement.

"Cohabitation is here to stay," says David Popenoe, a Rutgers sociology professor and report co-author. "I don't think it's good news, especially for children," he says. "As society shifts from marriage to cohabitation — which is what's happening — you have an increase in family instability."

Cohabiting couples have twice the breakup rate of married couples, the report's authors say. And in the USA, 40% bring kids into these often-shaky live-in relationships.

"It is important now to think beyond the divorce rate to other kinds of couple unions and look at how stable they are," says Barbara Dafoe Whitehead, a social historian and report co-author.

"It's a pretty short period of time for that change (cohabitation) to have occurred and to have taken hold in the way it has," she says.

In the USA, 8.1% of coupled households are made up of unmarried, heterosexual partners. Although many European countries have higher cohabitation rates, divorce rates in those countries are lower, and more children grow up with both biological parents, even though the parents may not be married, Popenoe says.

The USA has the lowest percentage among Western nations of children who grow up with both biological parents, 63%, the report says.

"The United States has the weakest families in the Western world because we have the highest divorce rate and the highest rate of solo parenting," Popenoe says.