Gallup used a methodology to mitigate that problem in their polling. The percentages of these polls range from about 3.4% to 3.8% for the entire LGBT demographic (including bisexuals married and unmarried): Special Report: 3.4% of U.S. Adults Identify as LGBT
One funny thing about that poll is that they also questioned people to see how much of the population they thought was gay. It turned out that young people under the age of 25 believed that 30% of the population is gay, when in reality it's only about 1% when discounting bisexuality. Basically the media has brainwashed these poor ignorant kids into believing that homosexuality is far more prevalent than it really is. It's a rare disorder that basically only affects a tiny segment of the population but through bullying tactics and intimidation the left has made into this huge monster of an issue.