TheColu.mn looked at polling from the last 8 years on the anti-gay marriage amendment, support for marriage equality and support for relationship recognition for same-sex couples. The trend is clear: more Minnesotans are supporting rights for same-sex couples and fewer support imposing a ban on marriage equality.

Anti-gay Amendment

Polling on whether Minnesotans support or oppose a constitutional amendment defining marriage as between one man and one woman has occurred since the issue was first brought before the Minnesota Legislature in 2004. TheColu.mn has included all polling on the amendment including those commissioned by supporters and opponents of the amendment (hence some of the spikes and valleys). These are just quick and dirty charts, i.e., no adjusting for time periods, different polling methods, etc.

Relationship rights

Support for relationship rights for same-sex couples has steadily increased over the past 8 years while those who say gay couples should have no rights has declined. Support for gay marriage has increased a bit but has not yet reached 50 percent.

Should gay marriage be legal?
Over the past 8 years, those who say same-sex marriage should be illegal has declined from a high in the 60s to just under 50 percent.

2012
Currently, the amendment can be viewed as a statistical tie. Only three polls have found the amendment above 50 percent this year. All three were KSTP/SurveyUSA polls. None have showed a majority of Minnesotans in opposition to the amendment. But there are a number of factors that could make the polls less of an indicator for the actual indicator of the outcome.

Minnesota’s constitution required a majority of all votes cast on an amendment in order for it to pass. If a voter skips the question, it counts as a “no.”

Hamline University Prof. David Schultz recently looked at the undervote on constitutional amendments in the past.

Going back to 1988 and looking at the last 12 amendments, the undervote averages 4.84%. It ranged from a high of 7.68% to a low of 0%. Why is this important? One needs potentially to subtract 5% from any support for constitutional amendments because some people will vote in the election but not on the amendments. It is possible that there will be a similar 4.84% average undervote on one or both of the amendments, but it is also possible it will be lower because both are politically salient and controversial. My guess is an undervote of about 2%. This means subtract 2% from support and then add 2% to opposition.

When looking at the polls, that suggests a 4 point swing toward the “no” side.

But, researchers have found that polls on marriage amendments almost always undercount the actual level of support.

In his 2010 paper (PDF) on the subject, Prof. Patrick Egan noted that in just about every case, people state polls found more opposition to an anti-gay marriage amendment than what actually existed when voters went to the polls. The discrepancy is unexplained: whether people lied to pollsters or some other factor played a part is unclear.

Egan notes: “However, polling consistently under-predicted the level of opposition to the legal recognition of same‐sex couples, with the actual vote in favor of banning same-sex marriage typically running about three percentage points ahead of projections drawn from pre-election surveys.” 
 
For instance, when Wisconsin voted on the issue in 2006, the poll underestimated support for the amendment by 3.5 percent.

Do these to factors, undervotes at the ballot box and overcounts by pollsters of the opposition, cancel each other out? That question will be answered on election day.

Earlier this year, polling analyst Nate Silver looked at the potential likelihood of a marriage amendment to be defeated in all 50 states. Of Minnesota, he wrote:

The Minnesota measure, which would ban same-sex marriage but not domestic partnerships, should be considered something of a tossup. Under the Accelerated Model, it would fail with about 49 percent of the vote, while under the Linear Model it would pass with 54 percent — both forecasts well within the models’ respective margins of error.

In other words, according to every poll, analysis

In 2009, Silver did an analysis that predicted that the earliest that Minnesota would vote against an anti-gay marriage amendment is 2013.

If the amendment passes in November, it won’t be long before there are enough voters willing to repeal it — at least according to polling over the last 8 years.