The Daily Beast today published some rankings saying that Dallas is the 19th-gayest city in the nation.

Everybody loves rankings, and the story has already been picked up by The Dallas Observer.

But here’s the problem: By the study author’s own admission, these statistics aren’t terribly accurate. That’s because they’re based strictly on the number of same-sex couples who identified as such on the U.S. Census Bureau’s 2008 American Community Survey.

In other words, the data doesn’t include single gays and lesbians, who are far more likely to live in big cities than in places like Springfield, Mass., or Ithaca, N.Y. — which both finished ahead of Dallas on this list.

From my column in 2007 about the results of the 2006 rankings:

According to the study, Fort Worth had 8.51 same-sex couples per 1,000 households from 2004-06, ranking it “23rd-gayest” of the nation’s 50 largest cities, according to the study.

Dallas, meanwhile, had 8.50 same-sex couples per 1,000 households, ranking it 24th. (San Francisco led the way, with 28.72 same-sex couples per 1,000 households.)

This marks a big change since 2000, when Dallas was 12th and Fort Worth 34th, and an even bigger one since 1990, when Dallas was 17th and Fort Worth 45th. Fort Worth, Jacksonville, Fla., and Louisville, Ky., have made the three biggest climbs in the rankings since 1990.

The fact is, though, there doesn’t appear to be any really good way to compare how many gays and lesbians live in various cities throughout the U.S.

While there’s no doubt Fort Worth has become more gay-friendly in the last 17 years or that Dallas has lost a lot of gay people to the suburbs, the author admits the rankings may be somewhat misleading.

For one, the study doesn’t include single people.

“I think we should always remember that we’re basing this only on the location decisions of couples, and we’re basing it on out couples,” said author Gary Gates, senior research fellow at the Williams Institute on Sexual Orientation Law and Public Policy at the University of California, Los Angeles.