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Back in April, I conducted an analysis of the prospects of a gay marriage ban becoming law in each of the 50 states. The analysis found that support for gay marriage bans was strongly tied to two factors: the degree of religiosity in a state, as measured by 2008 Gallup tracking surveys, and the year that the initiative was up for vote — marriage bans have lost support at a rate of about 2 percent per year, ceteris paribus. That analysis concluded that a Maine is one of 11 states that would probably vote to reject a ban on gay marriage if a referendum were held this year.

Mainers, in fact, will soon have a chance to test this proposition. In November, they will go to the polls to vote on Question 1; a yes vote would overturn a law passed earlier this year by the state’s legislature that permits gays and lesbians to get married in the state.

I decided to re-visit my model, which consists of a relatively simple data set of all previous anti-gay marriage initiatives. 31 of 32 such initiatives have passed, the sole exception being Arizona Proposition 107, which failed in 2006, although Arizona’s voters decided two years later to approve a similar measure that limited its scope to marriage rather than civil unions. I’ve expanded the model to include a new variable, which — pursuant to the Arizona case — is whether the initiative sought to ban civil unions in addition to marriage. (Although I’d given this a cursory look before, I evidently wasn’t careful enough, because it turns out to be highly statistically significant). I then placed the initiatives into a regression model, which yields the following results:

Bangay is the percentage of the vote in favor of the marriage ban; this is the dependent variable. The independent variables are year, which is the number of years elapsed since 1998, relig, which is the percentage of the state’s residents that consider religion “an important part of [their] daily lives”, and civil, which is whether the initiative sought to ban civil unions in addition marriage.

All three variables are highly statistically significant. Support for the marriage ban rises nearly one-for-one with religiosity; it falls by about two points (actually, 1.9) for each passing year, and it falls by 5-6 points if the amendment seeks to ban civil unions in addition to marriage.

Maine is the third least-religious state in the country, according to Gallup, with only 46 percent of that state’s residents saying religion is an important part of their daily lives. That bodes well for those who are hoping the initiative fails; the comparable fraction in California, which passed Prop 8 last year, is 57 percent. We’re also another year down the line on a type of initiative that pretty reliably loses support with each passing election. On the other hand, Question 1 would not seek to overturn civil unions, which gives it a better chance of passing.

Throw Maine’s numbers into the model, and we come up with an estimated level of support for the ban of 43.5 percent, with 56.5 percent opposed. In other words, the model’s prediction is that the ban will fail. The standard error of the forecast (not the margin of error, which is larger) is 5.2 points. This implies that the marriage ban only has about an 11 percent chance of passing.

But don’t start counting your (gay) chickens yet, because there are a couple of additional circumstances that are relatively unique to Maine. One is that this is a standalone initiative in an off-year election in which voters will have few other things to consider. What sort of electorate will turn out? This precedent has previously occurred twice, in Texas and Kansas, both of which voted on marriage bans in 2005. That Texas and Kansas voted to approve the marriage bans is no surprise, but the margin was somewhat wider than the model predicted — 76 percent in Texas, rather than the prediction of 71 percent, and 70 percent in Kansas, rather than the prediction of 67 percent.

Arguably, that implies that an marriage ban will gain about another 4 points’ worth of support if it occurs in an off-year election. If that is the case, the projected support for the marriage ban is 47.5 percent, which means that it has a 32 percent chance of passing — about one in three.

It is debatable, however, whether the same ought to hold true in Maine. In Texas and Kansas, which are conservative states, the base electorate is particularly conservative, and it’s the base that comes out to vote in off-year elections. But Maine is a fairly liberal state, and it’s not clear where the base lies there. In 2006, a mid-term election, 26 percent of the Maine electorate identified itself as liberal, and 26 percent as conservative. In 2008, with a much larger turnout, the numbers were essentially unchanged: 27 percent liberal and 28 percent conservative. On the other hand, while 27 percent of Maine’s voters identified themselves as having no religion or an “other” religion in 2008, only 20 percent did in the lower-turnout year of 2006. On balance, I suspect the off-year status of the election is slightly more likely to help Question 1 than to hurt it — old people vote in off-year elections, for instance, and old people mostly don’t like gay marriage. But the effects are not what they might be if we were talking about a state like Oklahoma.

Another factor is that this is the first time that a state’s voters will be considering on a gay marriage bill that was actually affirmed by the state legislature. With the exception of Prop 8 — which was a response to court rather than legislative action — all of the other marriage initiatives have been preemptive in nature. In addition, unlike virtually all other initiatives, Question 1 would not seek to ban gay marriage in the state Constitution; it would merely overturn the legislature’s decision. I figure that the first contingency is probably slightly unfavorable to Question 1 second is probably favorable, but this is fairly speculative.

There have also been three polls conducted on the gay marriage ban, although one is somewhat out of date:

On average, the ‘No on 1′ position — which would preserve gay marriage — appears to be about 3 points ahead. It trails slightly, however, in the only poll of likely voters, which is the one from Research 2000 / Daily Kos.

Time to play oddsmaker: I’d lay about 3 to 1 against the marriage ban passing. But it’s liable to fairly close — clearly a winnable campaign for conservatives and a losable one for liberals, especially if the sort of complacency sets in that we saw in California*.

* With that said, the model predicts that Prop 8 should have gotten 54 percent of the vote in California when it actually got 52 percent. So it’s not clear if the No on 8 campaign deserves quite the flak that it’s gotten.

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