Anneli Rufus of the Daily Beast recently cites 15 specific studies on factors correlating with higher divorce rates. Thelink is at http://www.thedailybeast.com/blogs-and-stories/2010-05-19/15-ways-to-predict-divorce/ for details, but in brief:

You live in a red state
Frequent arguments about money
Parents divorced (40% higher); Parents divorced & remarried others (91% higher)
Smokers marrying nonsmokers
Having daughters, not sons
Religion: Evangelical, Catholic, non-Christian, or atheist
You live in a highest-divorce county
Second (or more) marriage for both spouses=90% more divorce
Wife 2 years older than husband or more
Below-average IQ
Certain reproductive organ cancers
Multiple births (twins or triplets)
Cohabitation — having lived with more than one partner before first marriage
Same-sex marriage

Interesting that only one on the list involves kids–the multiple births. From what I see out there, with kids or not, if the couple does not make the relationship a top priority it is less likely to go the distance. For parents it means keeping this as #1 as they raise kids, not the other way around. For childless, it’s the same. I have seen childfree couples that put their careers first and it is a major contributor to the demise of the relationship. Commitment and devotion to each other has go to be #1… ~L

As for who stays married longer, even if parents stayed married longer, it wouldn’t necessarily prove marital happiness. Lower class couples might break up any time the situation isn’t ideal, but middle-to-upper-class couples are more likely to stay together for reasons not related to marital happiness.

Example: People with kids may be staying together solely for the kids, so if their marriage lasts 25 years, that could just be how long it takes for the oldest kid to be out of college. (These days, the non-custodial parent could get slapped with a bill to pay for college, but parents who stay married aren’t forced to pay for college, so that’s a great incentive to stay together at least through college!). Even if it’s not a monetary incentive, fathers who really love their kids might be miserable at the idea of only seeing them every other weekend and thus stay, unhappily, just to have more time with them.

I would also venture a guess that people with children are move likely to be religious and thus might stay together for religious reasons. I have a childhood friend who is married to a total bum who is useless and not all that nice of a guy, but she won’t leave him because her church and family frown on divorce. A couple of my super-religious sisters have rather lousy husbands, but are still married 20+ years later because their religion and social snobbery.

By contrast, a childfree couple obviously isn’t staying together for the kids, and in general, I find childfree people to be less religious and the ones who are religious are less likely to be in the more restrictive religions that would make you feel bad for divorcing (since those religions are also less likely to tolerate childfreedom).

One could also factor in that childfree women are more likely to have a career of their own, so they don’t feel so trapped in a bad marriage as, say, a woman who has no career or income of her own and wouldn’t have an easy time of leaving. Childfree men might have an easier time leaving, too, knowing they won’t get hit up with child support.

Since the marriages are in no way equal, the divorces would be in no way equal, thus it’s pretty difficult to compare.

If you showed me two couples celebrating their 20th wedding anniversary today and one had kids and one didn’t, I’d guess that the childfree couple was still happy or they wouldn’t still be together. The other couple? I couldn’t even venture a guess if they were happy or not.