SAN FRANCISCO, USA (AP) — How many gay men and lesbians are there in the United States? Gary Gates has an idea but acknowledges pinpointing a solid figure remains an elusive task.

Gates is demographer-in-residence at the Williams Institute on Sexual Orientation Law and Public Policy, a think tank based at the University of California, Los Angeles. For the institute’s 10th anniversary this week, he took a scholarly stab at answering the question that has been debated, avoided, parsed and proven both insoluble and political since pioneering sex researcher Alfred Kinsey said in the 1940s that 10 per cent of the men he surveyed were “predominantly homosexual”.

Gates’ best estimate, derived from five studies that have asked subjects about their sexual orientation, is that the nation has about 4 million adults who identify as being gay or lesbian, representing 1.7 per cent of the 18-and-over population.

That’s a much lower figure than the three to five per cent that has been the conventional wisdom in the last two decades, based on other isolated studies and attempts to discredit Kinsey.

One reason, according to Gates, is that until recently, few surveys tried to differentiate respondents who identified as gay or lesbian from those who sometimes engaged in homosexual acts or were attracted to people of the same sex. All were lumped into the gay category.

“One of the major questions, when you think about how many (lesbian, gay, bisexual and transgender) people are there, is what do you mean by LGBT?” he said. “This shows there are pretty big differences between people who use the terms to label themselves versus sexual behaviour or attraction.”

Gates found, for example, that another 1.8 per cent of the adult population, or a little more than four million Americans, identifies as bisexual, according to his research brief published yesterday by the Williams Institute.

He also estimated that 19 million people, or 8.2 per cent of the population, have engaged in sex with a partner of the same sex. That includes all groups, such as gays, bisexuals and heterosexuals who have experimented with same-sex behaviour.

Another two studies, conducted by state agencies in California and Massachusetts, yielded what Gates thinks is the first credible estimate of the nation’s transgender population. He puts it at about 700,000 adults, or 0.3 per cent of the population.

Gates is the first to admit his figures are imprecise.

But because so few national population surveys have asked about sexual orientation and the ones that have were not conducted consistently over time, the data on which to base a firm conclusion does not exist, he said.

Government agencies and private researchers have been reluctant in the past to include questions about sexual orientation and gender identity in their surveys, deciding the issue was not worthy of inquiry or assuming participants would be reluctant to answer honestly.