Other than http://blog.xkcd.com/2010/05/03/color-survey-results/ and specific gender/sex studies, I haven't seen studies that make a distinction between gender and sex. Of course, if you want to make the distinction about biological sex, then you have to define which of the biological criteria and categories you're using, and even then you need more than two categories (http://linuxmafia.com/faq/Essays/marriage.html).
When someone asks if you are male or female, 99% will interpret it as "do you have a penis or a vagina?", not "do you identify as a man or a woman?", nor any other
You seem to suggest that my interpretation is arbitrary, while I think it is the most colloquial. Do you honestly think that a 15 year old girl/boy would see this thread and think "well I am neither of those"? Or are you just deconstructing a very straightforward question by its edge cases to prove some kind of point that I'm missing?
Other than http://blog.xkcd.com/2010/05/03/color-survey-results/ and specific gender/sex studies, I haven't seen studies that make a distinction between gender and sex. Of course, if you want to make the distinction about biological sex, then you have to define which of the biological criteria and categories you're using, and even then you need more than two categories (http://linuxmafia.com/faq/Essays/marriage.html).