Update: It turns out that the Michael LaCour and Donald Green study described here really was "miraculous": it wasn't true. Two other political scientists, David Broockman and Joshua Kalla, tried to conduct an extension of the study, and ran into a number of irregularities, not least an unusually high response rate among survey participants. When they contacted the survey firm they believed performed the study and asked to speak with an employee believed to have helped, the firm said it was unfamiliar with the project, had no employee by that name, and didn't have the capabilities to run many aspects of the study.

Eventually, LaCour confessed to "falsely describing at least some of the details of the data collection." Green retracted the study on his website and has requested that Science, the journal that published the study, retract it as well. LaCour was set to become an assistant professor at Princeton this July, but Retraction Watch's Ivan Oransky notes that this position has been scrubbed from LaCour's personal website.

In the interest of full disclosure, my original post describing the study is below. But in light of the retraction, don't believe any of its findings. See here for a longer explanation of how LaCour faked his data.

It turns out that good old fashioned human-to-human conversation really can change people's minds. A new experiment from political scientists Michael LaCour and Donald Green finds that a well-designed house-to-house canvass can turn same-sex marriage opponents around — and sometimes bring their friends on board too.

LaCour and Green surveyed 9,507 Los Angeles County voters, all of whom lived in precincts that voted in favor of Proposition 8 (the 2008 ballot measure which banned same-sex marriage in California), six times over the course of about two and a half months.

They then broke their households into five randomly assigned groups. One group was canvassed by a gay campaign worker armed with a script (from the LA Gay and Lesbian Center’s Leadership LAB, which ran the canvas) meant to persuade voters to support same-sex marriage. Another group was canvassed by a straight campaign worker with the same script. The next two groups were canvassed by a gay or straight campaign worker, respectively, but this time with a script arguing for the importance of recycling waste. The final group wasn't canvassed at all. LaCour and Green then surveyed each group five times, to see how their feelings on same-sex marriage and on gay people generally changed from the initial, pre-canvass survey.

The result was dramatic. As you'd expect, households that got the recycling message didn't change their views on same-sex marriage or gay people at all in response (they didn't even change their views on recycling!). But those getting the same-sex marriage script very quickly grew considerably more sympathetic toward gay people and gay rights. Before, respondents felt the same about same-sex marriage as Nebraskans; after, they felt the same as folks from Massachusetts. When the canvasser was gay, the results were even bigger. While straight canvassers's effect wore off over time, gay canvassers's didn't.

BEFORE, RESPONDENTS FELT THE SAME ABOUT SAME-SEX MARRIAGE AS NEBRASKANS; AFTER, THEY FELT THE SAME AS FOLKS FROM MASSACHUSETTS

Because of the timing of the study, they were able to see how the Supreme Court's decisions in US v. Windsor (which overturned the federal ban on same-sex marriage) and Hollingsworth v. Perry (which upheld a lower court ruling striking down Proposition 8, effectively legalizing same-sex marriage in California again) affected people's opinions. Here's their chart of people's views on same-sex marriage, before and after both the canvass and the Supreme Court rulings:

As you can see, the canvass led to an immediate uptick in support for same-sex marriage among those getting the same-sex marriage script, but not others. But the Supreme Court decision led to an increase for everyone, and an especially large increase for those getting the same-sex marriage script. Same goes if you look at people's general feelings toward gays and lesbians, something the survey also measured:

"The treatment not only increased policy support and warmth toward gays," LaCour and Green conclude. "It also set subjects on a path to further attitude change in the wake of the Court's ruling on behalf of gay plaintiffs."

LaCour and Green also had the smart idea to make sure all their respondents lived with at least one other respondent, enabling them to measure "spillover" effects of the canvass that occur when, say, a canvassed woman talks about the subject with her roommate. They found that canvasses from straight people didn't cause spillover effects, but ones from gay people did. If you send a gay canvasser with a persuasive script to a house, you not only change the views of the person who answers the door; you change the views of the people they live with:

Modern political science and political psychology can breed a certain nihilism about the possibility of convincing anyone of anything. Stanford psychologist Geoffrey Cohen has found that whether or not people support a political proposal has more to do with whether the party they're a member of backs it than its actual content. Dartmouth political scientist Brendan Nyhan and the University of Exeter's Jason Reifler have conducted multiple studies that show correcting people's incorrect views about, say, the presence of WMDs in Iraq or whether or not Barack Obama is a Muslim or whether or not vaccines are safe can actually backfire and make them hold their wrong beliefs even dearer. In that context, what LaCour and Green found here is kind of miraculous. People's minds, it turns out, really can change.