Same-sex marriage legalization associated with reduced anti-gay bias in the U.S.

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Bias declined more sharply in states where legislation was passed locally
Published: 15Apr2019

A new study of evolving attitudes toward gay marriage across the U.S. suggests that state legislation has had a significant impact in reducing anti-gay bias in many parts of the country.

The findings, published in PNAS, provide evidence that public policy can shape social norms and alter individuals’ attitudes, says senior author Eric Hehman, a professor in McGill University’s Department of Psychology.

In 2004, Massachusetts became the first U.S. state to legalize same-sex marriage. In the following years, 34 other states and Washington, D.C., would follow suit before the Supreme Court ultimately ruled, in June 2015, that same-sex couples could marry nationwide. Since then, polls have suggested that support for same-sex marriage has steadily increased.

Eric Hehman, who specializes in how individuals perceive one another and how stereotypes and biases influence behaviour set out to measure whether and how state legislation had an impact on anti-gay bias.

“The idea that norms shape attitudes has been around in social psychology for many years,” says Hehman. “We wanted to measure if laws and policies can also act as norms and potentially change deeply rooted biases.”

Since same-sex marriage was legalized in different states over the course of 11 years, Hehman’s team was able to map trends in anti-gay bias during this period.

By geolocating responses at Project Implicit - a website launched in 2002 that measures biases of respondents - Eugene Ofosu, a graduate student working with Dr. Hehman, examined changing regional anti-gay biases of about 1 million respondents during a 12-year period. The researchers compared these trends before and after state-level legalization of gay marriage in each state.

Though implicit and explicit bias against the gay community was decreasing or stable prior to same-sex marriage legalization, the researchers found that legislation supportive of this marginalized population caused anti-gay bias to decline at roughly double the previous rate.

In the 15 states that did not pass same-sex marriage legalization locally by contrast, Hehman found a “backlash effect.” In those states, anti-gay bias increased in the immediate aftermath of the Supreme Court ruling making gay marriage legal nation-wide.

One possibility, Hehman says, is that -- even though attitudes were shifting toward more acceptance of same-sex marriage, a tipping point of support had not yet been reached in those states for the majority to accept the federal ruling.

The study also suggests that attitudes and legislation may be mutually reinforcing: evolving attitudes toward same-sex marriage may have served as impetus for both state and federal legalization.

“In other words, representative governments can contribute to and/or intensify change in the attitude of citizens by passing legislation,” Hehman says. “We have some evidence that the laws caused this changed in bias, but it is possible the effect goes in both directions.”


“Same-Sex Marriage Legalization Associated with Reduced Implicit and Explicit Anti-Gay Bias”, by Eugene K. Ofosu et al. will be published in PNAS on April 15th, 2019.

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