Research Focus of the Urban Institute. Recent Findings.
"Since the U.S. Census Bureau asks no questions about sexual orientation or behavior, how do researchers identify gay men and lesbians? The Census form does ask about relationships between individuals in the household, including husband/wife, son/daughter, brother/sister, and so on. For the first time in 1990, the Census Bureau also added an "unmarried partner" category. If the person filling out the census form designates another adult of the same sex as his or her unmarried partner, the couple is counted as a same-sex unmarried partner household. Research strongly indicates that the same-sex unmarried pair identified by the census are, in fact, gay and lesbian couples.
The way data is edited once it's collected changed in Census 2000 too. In 1990, when another adult of the same sex as the householder was identified as a "husband/wife," the couple was counted as a heterosexual married couple. In 2000, the "husband/wife" was counted as an "unmarried partner." Counting these same-sex married couples along with the same-sex unmarried partners helps explain the dramatic upsurge in the same-sex couple counts between 1990 and 2000. An even bigger factor may be the growing willingness of gay men and lesbians to identify themselves as partners."