Hey there, Matt:
I got this line from Wikipedia explaining the culture of San Diego: "San Diego had a gay index of 186 (gay male index of 226 and a lesbian index of 144); the national average gay index is 100." How do they come up with a "gay index"? Is the math as complex as a quarterback's rating? Or the Padres' team batting average?
-- A Gay Man in "Squaremont"
The math is pretty simple. Maybe too simple. It might not be the pinnacle of demographic science, but here goes... Gary Gates, a demographer now with the Urban Institute and author of The Gay and Lesbian Atlas, started the whole thing, later teaming with regional economist Richard Florida, author of The Rise of the Creative Class. Gates took year 2000 U.S. census data for selected metro areas, compared the number of households that were (self-reportedly) headed by same-sex partners (two gay men or two lesbians), then compared those figures to the number of traditional households in the same area. From this he produced a "gay index" number for each metro area. Over 100 on the index means the area contains more same-sex households than the U.S. average, and vice versa. That, basically, is the gay index. (The "gay" figure does not include un-partnered gays and lesbians in an area, since individual orientation is not reported on the census form.) Interesting, maybe, but was it useful?
Gates solved that by going to the Milken Index, a ranking of U.S. high-tech (IT and biotech) companies based on their longevity, economic growth, innovation, and other business factors. The better a company rates in all the factors, the higher it ranks on the Milken scale. Gates compared the top Milken companies (and their metro areas) to the metro areas with the highest gay indices and found some interesting matches. In 2001, the Brookings Institution published Gates's and Florida's findings, in which the authors stated, "The most statistically reliable indicator of a successful high-tech-friendly environment is the size and vitality of the gay population." Eleven of the top 15 high-tech companies and metro areas in Milken are also in the top 15 of the gay index.
According to the authors, a city's "open-mindedness" is the key. This fosters creativity, attracts creative and energetic people and creative companies, and generally makes for a more congenial environment -- good for the population, good for high-tech business. San Diego was congenial enough to rank fifth on the gay index, behind San Francisco/San Jose, D.C., Austin, and Atlanta. The gay index itself might be a valid descriptor, but expanding it to cause-and-effect sorts of relationships could be, statistically, a little too energetic and creative.