Much of the demographic data we have basically relies on self-report of people who are even willing to take a survey in the first place. We also don't (yet) have a technique to quantitatively or qualitatively assess female sexuality (with maybe the exception of homosexual women.) I also see issues where researches are trying to assess orientation in men and women in the exact same way. E.g. via plethysmography by showing them the same stimuli. Well, hate to break it to you, but it's pretty obvious that men and women do not use the same erotic material when they're given the choice.

On the overall, female sexuality is under-studied and under-theorized. We're asking for self-report, but we usually don't discern between several salient dimensions: identity, desire (and its quality,) and behavior.