A new study concludes that legalizing gay marriage has had no effect on the marriage rate among straight couples.

Researchers at Portland State University's School of Community Health examined opposite-sex marriage rates in the United States over the last 2 decades ending in 2009. Heterosexual marriage rates in states which had legalized civil unions or marriage for gay couples remained roughly the same as in states which prohibited such unions.

“This research shows that increasing legal recognition of same-sex marriage has no effects on rates of opposite-sex marriage in states that passed same-sex marriage laws,” said Alexis Dinno, lead researcher for the project. “Concerns about potential harm to the rate of opposite-sex marriage from same-sex marriage laws are not borne out by this research.”

Researchers described the claims of opponents that allowing gay couples to marry undermines the institution and discourages heterosexual couples from participating as “not credible.”

“Such claims do not appear credible in the face of the existing evidence, and we conclude that rates of opposite sex marriages are not affected by legalization of same sex civil unions or same sex marriages,” the researchers concluded.