While I do not have a study for you, I can tell you that we require two stalls for an efficiency or one-bedroom, three stalls for a two-bedroom, and four stalls for a three-bedroom unit. The problem we find is that almost every student has a car, and it is especially bad when they are over-occupied. At times we have used parking as a limiting factor to try to control occupancy. If there are only two parking spaces (with no on-street parking) it is less attractive to have three or more students in a unit. The other problem we sometimes get is students parking on lawns, but frequent citations seem to curb this pretty quickly at the beginning of the year.