So implies Nate Silver of 538 (h/t: Uncle) though he doesn’t quite come out and say that. Nate writes:

The table below details the divorce rates for the 43 states that reported their divorce statistics to the CDC in both 2003 and 2008. It is calculated by taking the total number of divorces in the state that year, and dividing it by the number of married persons, as reported by the Census Bureau. The result is then multiplied by two, since each divorce involves two people. This is different than how the divorce rate is sometimes calculated, which may be as a share of the overall population rather than the number of married persons; I prefer my approach because it will not penalize a state for having a lot of marriages (and therefore more opportunities for divorce).

I’ll grant Nate this much: calculating a state’s divorce rate as a percentage of the total population, rather than as a percentage of married people, is too stupid to consider. Of course the only divorce rate that means anything is the rate among those who could get divorced if they wanted to. Xrlq 2.0 and 3.0 both have zero divorce rates amongst them, but so what? The greater point, which Nate seems to overlook, is that the decision of certain couples to marry in the first place, and of others not to, is not random. In State A, where cohabitation is largely frowned upon, a marginally committed couple may choose to marry whilst a similarly situated couple in State B, where cohabitation is commonplace, may not. The likelihood of both couples breaking up is roughly the same, and probably much higher than the odds of a breakup between a more committed couple who would be married either way, but if both couples break up, the first couple will artificially inflate State A’s divorce rate vis a vis B.

Where Nate really goes off the deep end, though, is in distinguishing states whose laws simply do not provide for gay marriage from states whose voters have affirmatively acted to prohibit it:

Overall, the states which had enacted a constitutional ban on same-sex marriage as of 1/1/08 saw their divorce rates rise by 0.9 percent over the five-year interval. States which had not adopted a constitutional ban, on the other hand, experienced an 8.0 percent decline, on average, in their divorce rates. Eleven of the 24 states (46 percent) to have altered their constitutions by 1/1/08 to ban gay marriage experienced an overall decline in their divorce rates, but 13 of the 19 which hadn’t did (68 percent).

The differences are highly statistically significant. Nevertheless, they do not necessarily imply causation. The decision to ban same-sex marriage does not occur randomly throughout the states, but instead is strongly correlated with other factors, such as religiosity and political ideology, which we have made no attempt to account for. Nor do we know in which way the causal arrow might point. It could be that voters who have more marital problems of their own are more inclined to deny the right of marriage to same-sex couples.

The elephant in the room, which Nate scoots right by, is that constitutional bans on gay marriage have passed handily in every single state whose voters have been allowed to vote on them. Religiosity, political ideology, concerns about one’s own marriage, etc. may all play some role in determining the margin by which a constitutional or initiative ban on gay marriage may have passed in any particular state (a factor Nate does not examine) but the only factor determining whether a state has a ban gay marriage is the extent to which voters are or aren’t allowed to choose. Perhaps Nate’s real point is that if you allow people too much freedom of choice, they may choose to get a divorce?

It’s too bad that California is not included in the chart, as it would be the perfect state to prove whose theory is right. If mine is right, California should have a relatively low or declining divorce rate, as it’s a liberal state where uncommitted couples are free to shack up with little or no pressure to marry. If Nate is right, California’s divorce rate should be heading through the roof, as it’s the one state whose voters have acted not once but twice to prohibit gay marriage (though strictly speaking, CA hadn’t enacted a single constitutional ban as of 1/1/08, so perhaps Nate would skate on a technicality).