NYU (US)—Campaigns on ballot measures pertaining to the legal status of same-sex couples, including gay marriage, have minimal impact on voters, a new study finds.

“Most political scientists think that election campaigns do little, in the end, to move many voters one way or another,” says Patrick Egan, assistant professor of politics and public policy at New York University.

“This report indicates that ballot measures on same-sex marriage are no exception: neither advocates nor opponents tended to gain support in any consistent fashion in these campaigns, despite the millions of dollars spent by both sides over the past decade.”

The report, Findings from a Decade of Polling on Ballot Measures Regarding the Legal Status of Same-Sex Couples, is based on a compilation of the pre-election polls available in states holding votes on same-sex marriage and domestic partnership since 1988—a total of 167 surveys on 32 ballot measures.

Pre-election polls are consistently unreliable, the report says, because they underestimated voter support for bans on the legal recognition of same-sex couples.

Additionally, there is no evidence backing the theories that voters misrepresented their support for bans to pollsters, or that they were confused about the meaning of a “yes” or “no” vote.

The most notable finding Egan says, is that those favoring and opposing the ballot measures—have largely fought to a draw, meaning that the share of the public saying they intended to vote for or against these measures typically changed very little over the course of the campaigns.

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