Most Americans marry for keeps or, if it doesn't last, don't want to repeat the same mistake, according to new Census data that show 76% of those who have ever been married have married just once.

Almost 20% have been married twice and 5% have been married three or more times, finds data released Monday from the American Community Survey of 3 million households.

The survey also found almost 200,000 fewer same-sex couples than the previous year, which Census officials say resulted from data-processing changes. The total number of same-sex couples in 2008 was about 565,000, vs. 754,000 in 2007.

"We don't think Census is doing us dirty here," says Jaime Grant of the National Gay and Lesbian Task Force in Washington, D.C., which has been pushing for Census recognition of gay couples. "They improved the way they designed the form, so they got fewer false reports from opposite-sex partners. But I still think it doesn't mean we're getting the full picture of LGBT people across the board."

The new questionnaire format was meant to bring the annual survey more in line with the larger 2010 Census, said Martin O'Connell, chief of the Census' bureau's Fertility and Family Statistics Branch. "It was to promote a greater sense of consistency between the two," he says, adding that there was "no intention of altering in any way the estimates of same-sex populations."

The 2008 survey form and the upcoming 2010 Census form includes more detail, breaking down the numbers of those who are legal spouses or consider themselves such (about 150,000 couples), as well as those who call themselves unmarried partners.

For example, if someone chose "husband or wife" and a second relationship, just "husband or wife" would have been counted, suggesting in previous years — mistakenly creating a same-sex couple who said they were in a spousal relationship. Now, multiple check-boxes will yield a blank result and will be filled in later using a statistical formula based on area households.

The change is a step in the right direction, says isn't a surprise to demographer Gary Gates, of UCLA's Williams Institute, which studies sexual orientation law and public policy.

"I've been saying for the last five or six years there was a problem with the data collection — that they were counting different-sex married couples who checked the wrong sex box," he says. "It doesn't take that many mistakes to really contaminate the same-sex couples data."

Gates says he's co-authored several papers suggesting the data issues, with his most recent presented in April at a meeting of the Population Association of America in Detroit.

Grant says she hopes these new numbers will "give us a little bit of a wake-up call for how important it is for people in the community to make themselves visible on federal surveys like the Census and other surveys." she says.

Carl Haub, senior demographer at the non-profit Population Reference Bureau, based in Washington, D.C., says the new marriage data reflects trends around the world, including rising numbers of those who have never married. The 2008 data show the percentage of women 15 and over who have never married was 28.1%, up from 27.6% in 2007 and 27.3% in 2006.

Marriage duration is another new statistic, with the national average at about 18.2 years. "Many want to stay married until the children are independent or semi-independent," Haub says. "That certainly does make some sense. Some number people will stay together for the children. That timing might not be just a coincidence."

Contributing: Paul Overberg