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Toward gay marriage, two percent at a time

April 6, 2009 - 11:41 am

Nate Silver over at used the Iowa Supreme Court’s decision to allow same-sex marriages as an excuse to analyze voting behavior on the same-sex marriage issue over time. Silver analyzed polling data taken by Gallup before 30 different voter initiatives on same-sex marriage in various states. He made two important observations.


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.

This data fits neatly with the study conducted by the Gay and Lesbian Task Force shortly after Californians amended the constitution to ban gay marriage last year. That study concluded that pro-Prop. 8 voters tended to be defined by their church-going behavior and by their age more than other factors.


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.

Prop. 8 passed in California by roughly four points. Silver’s model predicts that if voters face the same-sex marriage question again in 2010, it will be a toss-up.

He goes on to list the year when different states will pass the tipping point in support of gay marriage, assuming his 2 percent per year rate holds true. Most of the New England states would approve a gay marriage measure right now, California will be ready by 2010, and Mississippi will be dead last, in 2024.

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