The most recent study about premarital cohabitation was conducted by researchers at the University of Denver (DU) and published in July 2009. The researchers conducted telephone surveys of couples who had been married for 10 years or less and asked about marital satisfaction and whether divorce had even been considered. According to their findings, 19 percent of the couples who'd lived together before marriage had contemplated divorce, compared with 12 percent of couples who'd lived together after their engagement and 10 percent of couples who didn't share space until after marriage [source: Bryner]. Additionally, the couples who lived together pre-marriage reported lower levels of marital satisfaction. The DU results are consistent with other studies on the subject, which have found a similar risk for divorce and poorer communication and problem-solving skills in couples who cohabited [source: Ambert].
DU researcher Scott Stanley posits that these cohabiting couples get married for the wrong reasons; rather than making a decision about commitment, couples who live together may find themselves "sliding" into marriage because it's easy to do so [source: DU]. After all, once you have a joint lease and a shared dog, who wants the hassle of a breakup? That may be why couples who move in together after getting engaged but before getting married are immune to the cohabiting curse -- they've already made a deliberate decision about their shared future.
According to DU, couples who live together to see if marriage is a good idea may be most prone to later disaster. It's possible that if you feel the need to "test" the relationship, you may already know in your heart of hearts that it's not meant to be. It's also likely that people who move in together have different values than those who don't; if you're very religious, you're less likely to cohabit, but you're also less likely to consider divorce an option when times get tough [source: CNN]. Cohabiters may be more apt to divorce, particularly if they've lived with several people in the past -- one study found that serial female cohabiters have divorce rates that are twice as high as women who cohabited once, with the man that became their husband [source: Wiley-Blackwell].
Whether it's your first or your 21st cohabitation, it's important to have a serious talk with your partner about moving in together. Make sure you're both on the same page as to what the step means for your relationship; after all, you probably don't want to slide into marriage with someone who only views living together as an easy way to skimp on rent.