My school in general is different anyway as people don't generally come in as a freshman with the idea of going greek we take a lot of transfer juniors and sophomores so pledge classes contain a lot of people... becuase of this though we have a lot of turn around also.. (with sisters leaving after only two year if they started as a junior) People also transfer a lot... EVEN so three of the ladies I pledged with are still around (although one had a hiatus at JC to up her GPA) but I am the only one who has graduated.... but we genreally initiate all of our women every semester... ( at least the two and a half years I was active we never had a new member drop) but then after that is when we start losing them if we're going to... transferring, disaffiliation etc.. but I'd say we keep about 90% of freshman who join until they are seniors...
I don't know... but it seems to me at schools where being greek is THE thing to do/be that if you don't you feel like an outcast so of course you're going to do it even if you don't really care to make the committment... so of course a lot of the members aren't going to stick around if they just joined out of social pressure really instead of genuine interest in belonging to the greek community.