Anti-LGBT+ biases dropped significantly as same-sex marriage was being legalized across the United States, according to new research looking at the link between attitudes and policy change.
Biases declined both in states that legalized gay marriage and in states that did not, said research by McGill University, published in the journal Proceedings of the National Academy of Sciences.
Massachusetts was the first U.S. state to legalize same-sex marriage in 2004, followed by 34 others, before the U.S. Supreme Court made same-sex marriage legal nationwide in 2015.
The researchers looked at attitudes among one million Americans over that 12-year stretch, using methods of measuring bias among volunteer participants.
One method utilized positive and negative word association with gay and straight people and the other asked participants to rate their feelings toward gays and lesbians.
The research, published on Monday, found rates of decreasing anti-gay bias nearly doubled in states where same-sex marriage was approved.
"Our work highlights how government legislation can inform individuals' attitudes, even when these attitudes may be deeply entrenched and socially and politically volatile," said senior author Eric Hehman, psychology professor at Canada's McGill University.
But because bias was decreasing or plateauing generally at the time, it is unclear whether less bias helped the legalization or if legalization led to less bias, researchers said.
"Probably what's happening is a groundswell of movement leading to the law being changed in the first place," Hehman told the Thomson Reuters Foundation.
"I speculate that if anti-gay bias was on the rise everywhere, lawmakers wouldn't be compelled to implement these laws," he said.
Research released in 2017 by the Pew Research Center, a non-partisan think tank, also showed a steady increase in approval of same-sex marriage to 63 percent in 2017 from 35 percent in 2001.
Bias spiked in states that had not approved same-sex marriage after the nation's highest court handed down its 2015 ruling, the research found.
"When a law is imposed upon you from afar, there's local resistance to that," Hehman said.