A San Francisco-based foundation released a study Tuesday that shows that voters nationwide don't change their minds during the course of an election campaign on whether to approve a ban on same-sex marriage.
Patrick Egan, an assistant professor of political science at New York University, said the study looked at whether ballot measure campaigns "change voters' hearts and minds in a particular direction."
"That just doesn't happen," Egan said.
The study examined more than 100 polls taken in the six months before votes on ballot measures on same-sex marriage and domestic partnership in 32 states between 1998 and 2009. In most of the elections, including one on California's Proposition 8 in 2008, voters approved a ban on same-sex marriage.
Egan said, "This report indicates that neither advocates nor opponents (of same-sex marriage) tended to gain support in any consistent fashion during these campaigns, despite the millions of dollars spent by both sides over the past decade."
The study, which was the focus of a news conference in San Francisco, was conducted by Egan and commissioned by the Evelyn and Walter Haas Jr. Fund, a private foundation that has among its goals the advancement of gay and lesbian rights.
Representatives of gay rights groups said the lesson they draw from the study is that an attempt to influence citizens to support same-sex marriage needs to begin well before an election campaign.
Kate Kendell, executive director of the San Francisco-based National Center of Lesbian Rights, said, "Clearly, the time to change hearts, minds and votes to support equality is before a campaign starts."
Egan said the study didn't show what would happen if one side simply didn't participate in a campaign on the issue, but noted, "No political scientist would say just put down your guns" if the other side has a well-funded campaign.
Egan said a second finding of the study is that polls consistently underestimate the number of people who will vote in support of a ban on same-sex marriage.
He said the percentage of people who voted to ban same-sex marriage during the past decade was typically about 3 points higher than the percentage shown in polls.
Egan said the reason for that is unknown but he speculated that it may have to do with the way pollsters screen likely voters.
The professor said the phenomenon suggests that same-sex marriage advocates "need to be ahead by a healthy margin in the polls in order to have a chance for victory in any traditional campaign."