"Forced" prefs?

[AlphaXi_Husky]

Originally Posted by FSUZeta

maybe it has to do with the number of chapters at a college and the # of pnms. As Shirley pointed out, Texas and Bama have 3 prefs, as does FSU, Florida, Georgia, Auburn, and I am sure many more that I can't think of right now.

I know U.Washington has three prefs, which has been the case for many years. I thought there was some sort of formula or recommendation to be followed regarding how many pref parties a campus should have, based on how the schedule from the rest of the week is - maybe from the MOI? Does anyone know more (or have any clue what I'm thinking of)?