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Nate Silver models marriage by the numbers, or, how to quantify inevitability | Hunter of Justice

Nate Silver models marriage by the numbers, or, how to quantify inevitability

by on April 6, 2009  •  In Marriage, Social science

The famed numbers geek of electoral projections – Nate Silver over at 538 – has turned his sights on legalization of same-sex marriage. For each state, Silver predicts which year a majority of voters would reject a ban on same-sex marriage (which could come earlier or later than a legislative majority to end the exclusion). My bet is that his analysis will become the new sacred set of numbers for lgbt advocates (which is good since that 10% of the population figure got debunked a decade ago).

How on target are these numbers? If folks in California put an initiative on the 2010 ballot to repeal Prop 8, we'll all find out – Silver says we'll win in '10. No one I've talked to who is on the ground in California agrees with that.

Map Scroll (anonymous) converted Silver's projections into this map:

Future+gay+marriage+map

Following is Silver on the inevitability of same-sex marriage:

I looked at the 30 instances in which a state has attempted to pass a constitutional ban on gay marriage by voter initiative. The list includes Arizona twice, which voted on different versions of such an amendment in 2006 and 2008, and excludes Hawaii, which voted to permit the legislature to ban gay marriage but did not actually alter the state's constitution. I then built a regression model that looked at a series of political and demographic variables in each of these states and attempted to predict the percentage of the vote that the marriage ban would receive.

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.

So what does this mean for Iowa? The state has roughly average levels of religiosity, including a fair number of white evangelicals, and the model predicts that if Iowans voted on a marriage ban today, it would pass with 56.0 percent of the vote. By 2012, however, the model projects a toss-up: 50.4 percent of Iowans voting to approve the ban, and 49.6 percent opposed. In 2013 and all subsequent years, the model thinks the marriage ban would fail.

Below are the dates when the model predicts that each of the 50 states would vote against a marriage ban. Asterisks indicate states which had previously passed amendments to ban gay marriage.

2009 (now)
Vermont
New Hampshire
Massachusetts
Maine
Rhode Island
Connecticut
Nevada*
Washington
Alaska*
New York
Oregon*

2010
California*
Hawaii
Montana*
New Jersey
Colorado*

2011

Wyoming
Delaware
Idaho*
Arizona*

2012
Wisconsin*
Pennsylvania
Maryland
Illinois

2013
Michigan*
Minnesota
Iowa
Ohio*
Utah*
Florida*

2014
New Mexico
North Dakota*
Nebraska*
South Dakota*

2015
Indiana
Virginia*
West Virginia
Kansas*

2016
Missouri*

2018
Texas*

2019
North Carolina
Louisiana*
Georgia*

2020
Kentucky*

2021
South Carolina*
Oklahoma*

2022
Tennessee*
Arkansas*

2023
Alabama*

2024
Mississippi*

The model predicts that by 2012, almost half of the 50 states would vote against a marriage ban, including several states that had previously voted to ban it. In fact, voters in Oregon, Nevada and Alaska (which Sarah Palin aside, is far more libertarian than culturally conservative) might already have second thoughts about the marriage bans that they'd previously passed.

By 2016, only a handful of states in the Deep South would vote to ban gay marriage, with Mississippi being the last one to come around in 2024.

It is entirely possible, of course, that past trends will not be predictive of future results. There could be a backlash against gay marriage, somewhat as there was a backlash against drug legalization in the 1980s. Alternatively, there could be a paradigmatic shift in favor of permitting gay marriage, which might make these projections too conservative.

Overall, however, marriage bans appear unlikely to be an electoral winner for very much longer, and soon the opposite may prove to be true.

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