Nate Silver is teh awesome

Here's his take on passing gay marriage bans:

It turns out that you can build a very effective model by including just three variables:

1. The year in which the amendment was voted upon;
2. The percentage of adults in 2008 Gallup tracking surveys who said that religion was an important part of their daily lives;
3. The percentage of white evangelicals in the state.

These variables collectively account for about three-quarters of the variance in the performance of marriage bans in different states. The model predicts, for example, that a marriage ban in California in 2008 would have passed with 52.1 percent of the vote, almost exactly the fraction actually received by Proposition 8.

Unsurprisingly, there is a very strong correspondence between the religiosity of a state and its propensity to ban gay marriage, with a particular "bonus" effect depending on the number of white evangelicals in the state.

Marriage bans, however, are losing ground at a rate of slightly less than 2 points per year. So, for example, we'd project that a state in which a marriage ban passed with 60 percent of the vote last year would only have 58 percent of its voters approve the ban this year.

All of the other variables that I looked at -- race, education levels, party registration, etc. -- either did not appear to matter at all, or became redundant once we accounted for religiosity. Nor does it appear to make a significant difference whether the ban affected marriage only, or both marriage and civil unions.

His model predicts that in 2012, Iowans would be split 50-50. This is the earliest that a gay marriage ban could possibly come up for a vote. By 2013, the model predicts the majority of voters will be against the gay marriage ban. This is the earliest that the ban is likely to come before Iowa voters, as the Democratically controlled legislature is unlikely to pass such a ban this year.