were about 601,209 same-sex unmarried partner households. In the United States, according to a report by The Williams Institute in April 2011, 3.5% or approximately 9 million of the adult population identify as lesbian, gay, or bisexual. A 2013 study by the CDC, in which over 34,000 Americans were interviewed, puts the percentage of self-identifying lesbians and gay men at 1.6%, and of bisexuals at 0.7%. In October 2012, Gallup started conducting annual surveys to study the demographics of LGBT people, determining that 3.4% (±1%) of adults identified as LGBT in the United States. It was the nation's largest poll on the issue at the time. In 2017, the percentage was estimated to have risen to 4.5% of adults, with the increase largely driven by millennials. The poll attributes the rise to greater willingness of younger people to reveal their sexual identity. A survey by the U.K. Office for National Statistics (ONS) in 2010 found that 95% of Britons identified as heterosexual, 1.5% of Britons identified themselves as homosexual or bisexual, and the last 3.5% gave more vague answers such as "don't know", "other", or did not respond to the question. Reliable data as to the size of the gay and lesbian population are of value in informing public policy. For example, demographics are of help in calculating the costs and benefits of domestic partnership benefits, of the impact of legalizing gay adoption, and of the impact of the U.S. military's former Don't Ask Don't Tell policy. Further, knowledge of the size of the "gay and lesbian population holds promise for helping social scientists understand a wide array of important questions—questions about the general nature of labor market choices, accumulation of human capital, specialization within households, discrimination, and decisions about geographic location." Measuring the prevalence of homosexuality presents difficulties. It is necessary to consider the measuring criteria that are used, the cutoff point and the time span taken to define a sexual orientation. Many people, despite having same-sex attractions, may be reluctant to identify themselves as gay or bisexual. The research must measure some characteristic that may or may not be defining of sexual orientation. The number of people with same-sex desires may be larger than the number of people who act on those desires, which in turn may be larger than the number of people who self-identify as gay, lesbian, or bisexual. Psychology The American Psychological Association, the American