Number crunching for the New York Times respected statistician Nate Silver has predicted that Minnesota’s 2012 ballot initiative to codify a ban on same-sex marriage in the state is likely, though not certain, to fail.
In 2009 Silver created a statistical model designed to predict “the percentage of the vote that gay marriage-related ballot initiatives will receive.”
Citing New York’s decision to legalize same-sex marriage, Silver has now revisited this model and has expanded upon it based on two primary assumptions:
The Linear Model assumes that support for same-sex marriage is increasing at the same rate every year;
The Accelerated Model utilizes a more optimistic trend from national polls on same-sex marriage.
The full analysis is supremely interesting, but is particularly so in reference to Minnesota’s 2012 referendum which, based on both versions of the model, would seem a close call.
Under the Accelerated Model, the amendment would fail receiving just 49 percent of the vote, yet by the more conservative Linear Model it would pass with 54 percent, both obviously within the models’ respective margins for error.
However, things are never quite that straightforward, and Silver highlights that there are some other factors to consider here.
One additional factor, however, is that Minnesota rules require a majority of all voters to cast a ballot in favor of a constitutional amendment in order for it to pass. So someone who turns out to vote next November and punches her ballot only for the presidential election is essentially a “no”¯ vote. Historically, about 5 percent of Minnesota voters undervote constitutional amendment proposals despite casting ballots for other races, so what this means is that the ban on same-sex marriage will de facto need something like 52 percent of the vote in order to pass. For this reason, I’d conclude that the Minnesota measure is a slight underdog.
In addition, the most recent poll in the state finds that 55 percent of voters oppose the ban on same-sex marriage while 39 percent support it. Polls on this issue have historically underestimated the support for bans on same-sex marriage but not by such a wide margin to account for this discrepancy. Instead, the rule of thumb is that you should assume that all undecided voters will vote for the marriage ban. But since an outright majority of Minnesotans oppose the initiative in the poll — even after accounting for the undecided — it provides some meaningful guidance.
The ban is certainly not a heavy favorite to be defeated: see this blog post for someone who thinks it will pass, and consider that there are two plausible Republican presidential nominees from Minnesota, which could affect the dynamics of the vote. But I’d set something like 5-to-3 odds against its passage.
North Carolina is also expected to consider an amendment to constitutionally enshrine a ban same-sex marriage and, unlike Minnesota, is predicted under both the Linear Model (60%) and the Accelerated Model (54%) to pass the ban. However, Silver points out that the text of the ban appears to also include domestic partnerships. This has historically been a handicap for such initiatives, meaning there is yet room for LGBT rights advocates to narrow that margin and capitalize on more recent liberal trends.
The analysis throws up some other talking points too.
A cautious Linear Model look at California suggests that 54 percent would vote down a constitutional amendment banning same-sex marriage. Similarly, 55 percent of voters in Oregon would refuse a ballot initiative on same-sex marriage today based on the more conservative Linear model.
However, Silver warns this analysis does not include a calculation for overturning a ban, only the likelihood of how voters would approach the question of banning same-sex marriage when asked now. Overturning a ban, while subtle distinction, may introduce different factors. Even so, this is interesting as California equality groups continue to flirt with the idea of a ballot initiative to overturn Proposition 8.
Iowa residents may be interested to hear that both models indicate that, if voting today, Iowa voters would vote to ban same-sex marriage in the state (52 or 58 percent of voters for the Accelerated and Linear models respectively). However, Silver points out this doesn’t account for the cumbersome ballot initiative process which makes any such effort unlikely to succeed until at least 2013 by which time, even by the conservative linear progression of support, the margins will have narrowed considerably to the point where Iowa voters may be swayed against a ban.
Talks of overturning New Hampshire’s same-sex marriage law would seem on even less fertile ground, with the public expected under both models to reject an amendment by as much as 60 percent.
While there are of course factors that can not be accounted for in such statistical readings, Silver’s predictions generally show that states with same-sex marriage on the books are unlikely to see a reversal, that states without gay marriage bans are overall unlikely to enact such a ban, and that as public support continues to increase more states would be expected to favor same-sex marriage.
How long that will take to translate into states overturning constitutional amendments or statutes banning same-sex marriage remains to be seen however.