This is a ranking of colleges, ordered by how difficult it is to be admitted to a college. The ranking is based on three important measures:
(i) The number of applicants for each admitted student, often called the "selectivity";
(ii) The average SAT score of entering students.
(iii) The high school ranking of admitted students, namely, what is the top portion of high school students that includes the students entering the college.

Here are the details:

(i) Using data reported by colleges, we calculate the number of applicants per admitted applicant by dividing the number of applications by the number of admitted applicants.
(ii) Using data provided by colleges, we calculate the 'rarity' of the average SAT score of each school. Specifically, we calculate how many test  takers there are for each one receiving the average score of the college or higher. This number is derived from percentile data about the SAT scores, as provided by ETS (the company that produces the SAT).

The product of the numbers obtained in (i), (ii), and (iii) is related to the number of potential students competing for each seat at the college. This number is listed in the last column of the table as the "Admission Difficulty".

A higher admission difficulty means higher competition for each seat at the college, making it more difficult to be admitted. The table is listed in declining difficulty of admission: the college at the top of the table has the most difficult admission and the last college in the table has the easiest admission.