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Late last month, the Journal of Marriage and Family published a new study with a somewhat foreboding finding: Couples who lived together before marriage had a lower divorce rate in their first year of marriage, but had a higher divorce rate after five years. It supported earlier research linking premarital cohabitation to increased risk of divorce.

But just two weeks later, the Council on Contemporary Families—a nonprofit group at the University of Texas at Austin—published a report that came to the exact opposite conclusion: Premarital cohabitation seemed to make couples less likely to divorce. From the 1950s through 1970, “those who were willing to transgress strong social norms to cohabit … were also more likely to transgress similar social norms about divorce,” wrote the author, Arielle Kuperberg, a sociology professor at the University of North Carolina at Greensboro. But as the rate of premarital cohabitation ballooned to some 70 percent, “its association with divorce faded. In fact, since 2000, premarital cohabitation has actually been associated with a lower rate of divorce, once factors such as religiosity, education, and age at co-residence are accounted for.”

It’s not unheard-of for contemporaneous studies on the same topic to reach opposite conclusions, but it’s somewhat surprising for them to do so after analyzing so much of the same data. Both studies analyzed several cycles of the National Survey of Family Growth, a longitudinal data set of women (and men, starting in 2002) between the ages of 15 and 44, though Kuperberg’s study incorporates some data from another survey as well. And, this isn’t the first time researchers have come to differing conclusions about the implications of premarital cohabitation. The practice has been studied for more than 25 years, and there’s been significant disagreement from the start as to whether premarital cohabitation increases couples’ risk of divorce. Differences in researchers’ methodologies and priorities account for some of that disagreement. But in the curious, still-developing story of whether cohabitation does or doesn’t affect the odds of divorce, subjectivity on the part of researchers and the public may also play a leading role.

After a landmark study from 1992 suggested a link between living together and divorce, a flurry of subsequent studies investigated why this might be. Intuitively, a trial run of living together before marriage should increase the stability of a relationship. One such study questioned whether the relationship between cohabitation and divorce was a product of selection: Could it just be that people who were more likely to consider divorce an option were more likely to live together unmarried?

However, over the years, many researchers began wondering whether earlier findings that linked cohabitation to divorce were a relic of a time when living together before marriage was an unconventional thing to do. Indeed, as cohabitation has become more normalized, it has ceased to be so strongly linked to divorce. Steffen Reinhold, of the University of Mannheim’s Research Institute for the Economics of Aging, pointed out in a 2010 study that in European countries, the correlation disappeared when the cohabitation-before-marriage rate among married adults reached about 50 percent; the U.S. seems to have just gotten to this threshold. In 2012, a study in the Journal of Marriage and Family concluded that “since the mid-1990s, whether men or women cohabited with their spouse prior to marriage is not related to marital stability.” This is the same journal that just published a study finding the opposite.

Galena Rhoades, a psychologist at the University of Denver, has a few theories as to why it’s so difficult to glean what effect, if any, cohabitation has on marital stability. For one, she says, it’s hard to study divorce in ways that are useful and accurate, because the best data sets take so long to collect. Many people don’t get divorced until many years into their marriage, and the social norms around cohabitation in the U.S. have evolved quickly, so “if we study a cohort of people who got married 20 years ago, by the time we have the data on whether they got a divorce or not, their experience in living together and their experience of the social norms around living together are from 20 years ago,” Rhoades told me. In other words, by the time researchers have enough longitudinal data to know whether one is meaningfully linked to the other, the social norms that shaped the findings will hardly be of use to couples today trying to figure out how cohabitation could affect their relationship. Thus, Rhoades said, longitudinal studies tend to paint a full picture of the relationship between living together and divorce, while simultaneously telling Americans today little about the time they actually live in.

Rhoades believes that studies should take into consideration couples’ intentions when they move in together—something neither of the recently published studies does. As she and her colleague Scott Stanley have found in their own research, when analyzing only couples who move in together with the intention of getting married, and thus excluding those who eschew marriage or just want to save money on rent, the heightened risk of divorce disappears. That’s because living together—which often results in a shared apartment lease or ownership of a home, joint custody of pets, or at the very least a shared accumulation of stuff—makes breaking up a greater logistical challenge.

“Some couples move in together without really having a plan for their relationship, and they can ‘wind up’ getting married even though they may not have if they hadn’t been living together,” she says. Which in turn leads to a lower degree of marital satisfaction and a higher risk of divorce.

But as Justin Lehmiller, a sex researcher at the Kinsey Institute and the author of the book Tell Me What You Want, says, there might be more to the scholarly controversy over cohabitation than just disagreements about methodology or analysis.

“It’s not just that we’re talking about different outcomes; we’re talking about using the same data and showing different outcomes,” he told me. It comes down to: “Whose judgment do we trust more?”

One reason Lehmiller thinks premarital cohabitation may be controversial among researchers is because the practice is controversial in general. It has historically been culturally frowned upon—it is, after all, an unapologetic signal to the outside world that premarital sex is being had in a particular household. In many places, that stigma lingers today, which could give the studies linking it to unsuccessful marriages some staying power.

“Popular beliefs tend to die hard, even in the face of evidence that might disconfirm them,” Lehmiller said. “Some people might want to believe certain things about the impact of living together before marriage, maybe stemming from religious or moral beliefs.”

But Rhoades pushed back on the suggestion that some bias toward confirming researchers’ own beliefs may be at work. “In general that can be true in psychology and in sociology; any scientific field, I think that can happen,” she said. “But because there’s such heated debate, I would bet that good researchers are extra careful about what they wind up publishing.”

As researchers move toward a more nuanced understanding of what cohabitation means for the future of unmarried romantic partners, several factors urgently need to be considered, according to the experts I spoke with. Lehmiller said studies of cohabitation should start working with data sets that include same-sex couples and move away from equating the stability of a marriage with its success. “Some people have views about marriage that would lead them to stay in one even if it’s not satisfying,” he said. In other words, just because a marriage lasts doesn’t necessarily mean it’s the best outcome for either party.

Rhoades, though, believes that research should acknowledge the many simultaneous ways marriage itself is changing versus just couples’ living situations before they tie the knot. As the average age of when Americans marry rises, so does the average number of Americans’ sexual partners before marrying. People are simply experiencing more before committing to one partner for life, she said, and expectations of the institution are shifting accordingly. As the research on what makes people get married and stay married matures, it’s important for researchers to think about all those premarital experiences as having an aggregate impact on marriages and families. “Cohabitation is just one part of it,” she said. “There’s a larger landscape for us to be considering.”

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