your race, athletic ability, artistic ability,
Lets take Duke. The SAT range of admitted students is 1340 to 1530. (M+R) Thus if you have lets say a score of 1440 you believe that you should have an "average" chance of acceptance. (So if Duke admits 20% of all applicants then you have a 20% chance of admission)
One Admissions officer of a very popular well know state flagship said she could read an app in under 15 minutes--that they took the thousands of apps--and sorted by scores.