Sociologists think the calculus may have changed. Part of the difference stems from just who’s deciding to shack up. In the late ’70s, only about a third of people lived together before tying the knot. Those people tended to be less traditional in their beliefs—it was the age of the hippie, after all—and therefore more likely to get divorced, says Pamela Smock, a sociologist at the Population Studies Center at the University of Michigan, Ann Arbor. As cohabiting has come more common across the country, however, the once strong link between “living in sin” and divorce has weakened over time. While some religious groups, such as socially conservative Christians and Orthodox Jews, still frown upon living together before marriage, two thirds of marriages in the U.S. now start as cohabitations. “Something that used to be stigmatized is now becoming the common experience,” Smock says.

Another difference is why couples decide to live together. The ’70s-era domestic partners might have been motivated by free love. But as you might expect in an era of high unemployment and rising poverty rates, it’s often money, not romance, that prompts today’s couples to share an address. “What really stood out was the change in unemployment characteristics,” says Rose Kreider, a family demographer for the U.S. Census who analyzed recent data on the topic. In 2008, 59 percent of cohabiting couples said both partners were employed. That number fell to 49 percent in 2010. Kreider says the survey specifically asked people if they were living with a boyfriend or girlfriend.