For conservative families it was, and still is, unacceptable if you were to shack up with someone before marrying them because you'd be "living in sin," depending on how Catholic your family is. Also, they believed that this increased the risk of divorce.

But it turns out that 'playing house' actually lowers the divorce risk.

Statistics that show a correlation between cohabitation and divorce date back to the 1970s, and until now, social scientists didn't really have any conclusive evidence as to whether that correlation was actually causation.

Some surmised that people who move in without getting married are doing it for the wrong reasons. Their reticence to marry might have been due to a mental reservation about their partner, a desire to keep things open-ended, or maybe they just weren't truly committed to each other.

New research from the University of North Carolina-Greensboro shows that the premarital living arrangements have nothing to do with why couples get divorced. In fact, the biggest predictor for failed marriages are people who committed too early in life, before they were ready:

Previous studies compared the divorced rates of couples who cohabited with those who didn't by using the age of marriage. [Researcher Arielle] Kuperberg did something new: She compared the relationships using the date of first moving in together. That date, she reasoned, is when a couple really takes on the roles of marriage, regardless of whether they have a legal certificate.

Using this method, she found no link between whether people had cohabited before marriage and their rate of divorce.

The reason why people who cohabit were more likely to get divorced wasn't because they cohabited. It was because they were too young when they made a cohabitational commitment. So if you're too young when you get together, there might not be much that can save your marriage when you and your partner grow up and grow apart.

[Contemporary Families]