I used to consider a school really selective if it had a 25% or lower acceptance rate. However, the number of such schools has more than doubled over the course of this decade.
25% or below acceptance rate at start of decade:
Harvard
Yale
Princeton
Stanford
MIT
Cal Tech
Dartmouth
Brown
Columbia
Williams
Amherst
Swarthmore
Georgetown
Rice
http://collegeadmissions.tripod.com/...-1999-2000.txt
25% or below acceptance rate for most recent class:
Harvard
Yale
Princeton
Stanford
MIT
Cal Tech
Brown
Columbia
Dartmouth
Penn
Williams
Amherst
Swarthmore
Pomona
WUSTL
Middlebury
Bowdoin
Claremont McKenna
Cornell
Georgetown
Duke
Cal/Berkeley
Colgate
Notre Dame
UCLA
Rice
Haverford
Vassar
USC
Find a College - College Search - Majors and Careers
Is it the common app, more high school seniors (although college class sizes have increased slightly too), less high schools having class rank making students think they have a better chance, these colleges becoming better marketers or something else?