Answered on Quora.
Careful scientific study has shown that very small numbers of men and women are 50–50 bisexuals. Only 1% of the population are 50–50’s.
And even 40–60’s and 60–40’s are not at all common. For instance, only 1% of men are 40–60’s – bisexual with slight lean towards gay.
Most straight leaning bisexuals cluster over at the far end as 90–10’s and 80–20’s. Fact is though that most 90–10 and 80–20 men are simply going to identify as straight, which is really what they are anyway. In fact, 80% of bisexual men (defined as responding to both homo- and heterosexual stimuli in the lab) lean heterosexual.
Once again, almost all 10–90, 20–80, and even 25–75 men and women identify as gay or lesbian.
You have to get towards 70–30 and 30–70 to where people really start calling themselves bisexual. So yes, most bisexuals lean one way or the other.