sorority rankings calculation

It's a glorified high school popularity contest at best. Not decrying those who actually care, because Miami is a very sink-or-swim kind of place in terms of social competitiveness. But take it for what it's worth, because it's all based on looks, social ability, and a "who hangs out with who" mentality.

The person above is right that its looks and who hangs out with who, it's social hierarchy but the #1 thing that defines tiers is how well sororities do in rush. If all the PNMs love a sorority, the sorority gets to cut more girls and hand pick exactly what members they want. Some sororities get to be way more selective because they're so desired. Those "top" sororities also get members that all the other sororities wanted as well whether it's because they're smart, pretty, intelligent, good personality, whatever. The higher the return rates, the higher tier a sorority is. Also, involvement on campus definitely has a small factor in it.