Marriage advice and causation

This Yahoo! column lists ten keys to avoiding divorce. It also inadvertantly illustrates common confusions about the difference between correlation and causation.

Take the first one: a two-year courtship. I am sure it is true that courtships around this length have the lowest probablity of divorce. I am also sure that this relationship is not causal in general. Going from a very short courtship up to two years likely has some causal effect via the extensive margin - that is, by leading poorly matched couples to forgo their marriage plans. It may also have some positive causal effect on the intensive margin by allowing for greater discussion and agreement on the rules of the marriage before it starts. But simply taking two people who think it is a great idea to get drunk, drive to Vegas and get married and having them simply delay their drunken nuptials for a while seems unlikely to accomplish much. Similarly, very long courtships may be a sign of one partner being pushed into marriage, something the list itself suggests is a bad idea in point 10. This part of the relationship between courtship length and divorce probability seems likely to be all selection. An interesting thought question concerns where one might go looking for some exogenous variation in courtship length to use to sort all of this out empirically.

A similar point holds in regard to the living together issue in the second item. There is a literature on this. The literature, well, at least some of it, recognizes the difficulty in sorting out correlation from causation. The lack of exogenous variation on this front is a problem here too. Some sources of variation that might seem plausible, such as religion, are likely to affect divorce probabilities in ways other than through their effect on the probability of living together.

I will support the idea of talking about the big issues before you marry. Lisa and I did this and it had a very large payoff. We have recontracted away from some of the deals we made, but the pre-marriage deals gave us a starting point for the renegotiation that was very helpful. Popular culture emphasizes the romantic aspects of marriage, which are very nice indeed, but it is also an economic arrangement that involves team production of some goods like children and sex (not necessarily in that order), division of labor in the production of other things and so on. Making concrete decisions about these practical aspects makes the transition to marriage easier and also provides a lot of valuable information about your prospective partner.

My advice: negotiate seriously and bluntly before marriage and also be careful about advice columns.