Does living together before marriage increase or decrease the chance of divorce?

Via The New York Times:

In a nationwide survey conducted in 2001 by the National Marriage Project, then at Rutgers and now at the University of Virginia, nearly half of 20-somethings agreed with the statement, “You would only marry someone if he or she agreed to live together with you first, so that you could find out whether you really get along.” About two-thirds said they believed that moving in together before marriage was a good way to avoid divorce.

But that belief is contradicted by experience. 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.

And:

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.