ON KNOWING YOUR PARTNER IS THE TYPE WHO WOULD SHACK UP:

Couples who cohabit before marriage (and especially before an engagement or an otherwise clear commitment) tend to be less satisfied with their marriages -- and more likely to divorce -- than couples who do not. These negative outcomes are called the cohabitation effect.

Researchers originally attributed the cohabitation effect to selection, or the idea that cohabitors were less conventional about marriage and thus more open to divorce. As cohabitation has become a norm, however, studies have shown that the effect is not entirely explained by individual characteristics like religion, education or politics. Research suggests that at least some of the risks may lie in cohabitation itself.

As Jennifer and I worked to answer her question, "How did this happen?" we talked about how she and her boyfriend went from dating to cohabiting. Her response was consistent with studies reporting that most couples say it "just happened."

"We were sleeping over at each other's places all the time," she said. "We liked to be together, so it was cheaper and more convenient. It was a quick decision but if it didn't work out there was a quick exit."

She was talking about what researchers call "sliding, not deciding." Moving from dating to sleeping over to sleeping over a lot to cohabitation can be a gradual slope, one not marked by rings or ceremonies or sometimes even a conversation. Couples bypass talking about why they want to live together and what it will mean.

WHEN researchers ask cohabitors these questions, partners often have different, unspoken -- even unconscious -- agendas. Women are more likely to view cohabitation as a step toward marriage, while men are more likely to see it as a way to test a relationship or postpone commitment, and this gender asymmetry is associated with negative interactions and lower levels of commitment even after the relationship progresses to marriage. One thing men and women do agree on, however, is that their standards for a live-in partner are lower than they are for a spouse.

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