The list varies by college but it typically includes stuff like Ability to communicate orally , Written Communication , Intellectual Ability , Ability to conduct independent research , Judgement & Maturity ,etc... They need to rate you with in the pool of students they know as top 2% , top 5%, top 15 % and so on....... They will also asked to mention the comparison pool and size, After this they can submit an optional letter. I hope this helps
PS: The questions and rating scale are different for different colleges.