This subject has been debated since sex researcher Alfred Kinsey said in the 1940s that 10 percent of the men he surveyed were "predominantly homosexual." Later, a much respected University of Chicago study estimated the figure to be closer to the 3 to 5 percent and that oft cited figure has been the conventional wisdom in the last two decades.

One reason a better estimate has been difficult to judge , according to Gates, is that until recently, few surveys attempted 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. Gates found, for example, that another 1.8 percent of the adult population, or a little more than 4 million Americans, identifies as bisexual, according to his research brief published last Thursday by the Williams Institute.

He also estimated that 19 million people, or 8.2 percent 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 behavior.

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 percent of the population.

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