Public opinion surveys may be understating opposition to same-sex marriage due to social desirability bias, according to research published in American Politics Research in April.
The so-called Bradley effect first emerged in 1982, when Californian gubernatorial candidate Tom Bradley lost the election despite polls indicating he had a significant lead. Researchers found some white voters falsely claimed to support the African-American candidate because they feared appearing racially intolerant, a phenomenon dubbed social desirability bias.
Richard J. Powell of the University of Maine has found a similar effect was occurring amid the debate over same-sex marriage.
“It is difficult to say conclusively why social desirability bias continues to plague polling on same-sex marriage even as it has largely disappeared on issues of race and gender, but it is likely due to the fact that opinion change in the area of homosexual rights continues to lag behind those of race and gender relations,” Powell wrote in his study.
For his study, Powell analyzed statewide ballot measures regarding same-sex marriages and the corresponding opinion polls from 1998 to 2012. During this time period, 30 states had ballot measures to prohibit gay and lesbian couples from marrying. Another 3 states had ballot measures to legalize same-sex marriage.
He discovered that election day opposition to same-sex marriage was between 5-7 percent greater than indicated by preelection polls. Social desirability bias, and not some other factor like flawed polling methodology, appeared to have caused this effect. There was no significant discrepancy found between preelection polls and election day results for ballot measures regarding taxes, bond issues and term limits.
Powell explained in his study that social desirability bias increases “as opponents sense their opinions are becoming socially stigmatized.”
“At some point, as a new dominant consensus emerges, there are simply too few opponents remaining who might be susceptible to social desirability bias,” he continued.
If current trends continue and acceptance of gay, lesbian, transgender, and bisexual people grows, the “Bradley effect” for same-sex marriage will likely dissolve completely.
“This is a question that will be fascinating to study over time to see if it, indeed, turns out to be the case,” Powell concluded.