how many drop out?

Sorry if this is a dumb question, but just wondering, how many girls actually drop?

I follow about ~50 girls from here, mostly freshman, noticed quite a few go through rush but not bid any where. They are pretty girls and seem some what connected, I am assuming they just didn't like what houses they were down to and dropped.

Also noticed a few 5-6 girls transferring out of ole miss.

And read something about ole miss's 4 year graduation rate being at 55% and 6 year graduation rate at 60% or something like that...I don't remember the numbers but it was ridiculously low.

Someone told me a long time ago about 1/2 the girls drop but I never believed that.

So how many girls actually drop? I am counting as rushing and dropping because you didn't like your houses, transferring out and going to a house and dropping some time before graduation for whatever reasons (didn't like it, too much money, falling behind in school, etc.)