A San Francisco-based foundation released a study today 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."