Sex Change Operations: The Science, Sociology and Psychology – By Sally Law, LiveScience’s Science of Sex Columnist

Chaz Bono, as Sonny and Cher’s former daughter is now known, began a surgical process to become a man earlier this year, and in doing so, joined the increasing numbers of people who now undergo gender-reassignment surgery annually.

It’s difficult to gauge the size of the transgender population in the United States. The U.S. Census doesn’t record this data, and neither does any other organization – at least, officially. The National Center for Transgender Equality in Washington, D.C., estimates the number as between .0025 percent and 1 percent of the general population.