Supporters of a sex marriage bill hold signs as Senators...

Supporters of a sex marriage bill hold signs as Senators and others are interviewed outside the New York Senate Chamber. (June 17, 2011) Credit: Getty Images

If New York legalizes same-sex marriage, 42,600 gay and lesbian couples could be affected, a new report has found.

An estimated 21 percent of those couples are already legally married, taking advantage of laws in Canada and New England, according to the Williams Institute, a think tank at the UCLA School of Law.

"It seems to me allowing couples to marry in New York is just acknowledgment of that reality," said Gary Gates, a research scholar at the institute, which studies law and public policy on sexual orientation issues.

There are about 3,500 same-sex couples on Long Island, according to 2009 census estimates; 2010 census data on same-sex couples are due to be released later this year.

The institute based its analysis on 2009 American Community Survey data from the Census Bureau and a survey with Harris Interactive of 600 same-sex couples around the country.

Gates said the status options for same-sex couples on the 2010 Census form -- "unmarried partner" or "husband/wife" -- posed a problem for some.

Many same-sex couples who can't legally wed in their state of residence still consider themselves married, he said. Others may have received other forms of recognition short of marriage, forming civil unions or registered domestic partnerships.

The analysis found that nearly 9,000 couples in same-sex relationships in New York are already legally married. Gates placed the margin of error of that estimate at 6 percentage points.

The institute also reported that 7,200 same-sex couples in New York were raising about 14,000 children, citing 2008-09 census estimates.

According to the survey, 38 percent of same-sex couples living in states that allow them to marry have taken that step. The rate is 12 percent in states that haven't legalized same-sex marriage.

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