Apples to Apples

December 11, 2010 at 12:40 pm

| Gabriel |

At Slate’s XX blog, Amanda Marcotte discusses a report by Brad Wilcox (a good friend of mine from grad school) and basically asks if we can be sure that marriage actually benefits people or is it just selection:

Sure, marriage chauvinists can point to things such as marriage’s impact on health and well-being, and to the fact that married men are less anti-social. I’m skeptical, though, because these kinds of studies lump all nonmarried people into one group. People who are in long term, committed relationships without that piece of paper are put in the same group as people who’ve never held a relationship together. I want to see apples to apples comparisons. How do unmarried people who’ve been together for five or 10 years hold up next to people who have been together that long but tied the knot in their first year or two together?

Let’s put aside the fact that cohabitating couples are indeed different from married couples even holding constant duration. There’s an interesting question here and it has a lot to do with what you mean by “apples to apples” and how such commensuration works under different logical premises. The traditional approach is to throw controls at something. So following this logic, Marcotte is exactly right to say that we ought to be controlling for things like duration of the union.

However traditional (or common in scholarly practice) such an implication may be, it just ain’t right. Suppose that a couple in their mid-to-late twenties came to you and said, “We are deeply in love and committed to each other. We’d probably like to have children at some point. Given that we have no religious reasons to get married, should we marry or just move in together?” It would be silly to base your advice to this young couple on the expected quality of their union conditional on it not dissolving. The reason is that one of the worst things that is likely to happen to this couple is breaking up and all the ugliness this entails, especially if they have kids. If dissolution is much more likely if they are cohabiting then this is worth factoring in rather than assuming away. The total treatment effect of marriage versus cohabitation needs to count from formation forward and include all end states rather than using a cross-sectional sample of survivors (which from the viewpoint of formation is systematically censored) and using tenure as a variable. The same logic applies in more extreme forms to tournament model labor markets. If you want to know whether being a rock star is a good career aspiration you shouldn’t look just at rock stars but also at the far more numerous people who seriously pursued careers in pop music but nonetheless failed at it.

OK, let’s make a slightly more charitable argument and assume that Marcotte understands everything I just said but thinks that there is selection into cohabitation versus marriage such that most of these ephemeral cohabitations would have dissolved even if they were marriages. In particular she seems to have in mind some kind of selection on the unobservable of “commitment.” This is a fair point in part but unlikely to change anything much. First, if an unobservable is correlated with observables then omitted variable bias is mitigated. Second, something like unobservable “commitment” is likely to be a relatively ephemeral inclination and most of its impact should be early in the union whereas the hazard for dissolution of cohabitation remains persistently high rather than crashing after a few years like the hazard for divorce. We have support for this in qualitative data. Contrary to “that baby ain’t mine bitch” stereotypes, a very high proportion of unwed fathers express a commitment to a newborn child and (to a slightly lesser extent) the child’s mother. Nonetheless unless they marry the mothers, within a few years most of these fathers will have broken up with the mothers and an almost inevitable consequence of the dissolution is much less involvement with the child than the father initially expressed the intention to maintain. I’m generally inclined to think that accounts are as much cultural scripts as reliable articulations of preferences and logics of action, but the rich qualitative work in this area seems to have established that the men are sincere and so I’m willing to say that if you’re not convinced by the last 20 years of qualitative and quantitative demography that there really is a substantial treatment effect of marriage then the burden of proof is on you to prove that there’s not.

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