It can really sound like greater numbers of girls are lesbians or bisexual than ever before. But does that necessarily mean that there really are greater numbers? Dr. John Grohol, CEO and founder of Psych Central, doesn't think so. He responds in rebuttal to opposing views expressed by Leonard Sax in his blog "Sax on Sex".
Dr. Grohol observes that sexual mores have changed drastically in the past few decades. Greater tolerance exists now, concerning sexual preferences and practices than at any other time in our culture's history. People have less need to hide who they are and what they do.
"The simple and more probable explanation is found buried in Sax’s notes — that in different times, different standards were more acceptable. Therefore reporting of one’s sexuality is likely to be biased toward those standards. In other words, it’s not that there are necessarily more lesbians and bisexuals today, it’s that people feel far more free and open to identify with that label without as much fear of societal or criminal prosecution."
http://psychcentral.com/blog/archives/2010/04/12/are-more-girls-really-lesbian-or-bisexual