The UC system must keep statistics on the fail rate of lesser qualified entrants. I suspect it correlates well.
My son started this year at UCSD in engineering and was shocked at how many really smart people there were there.
He was pretty much accustomed to being a big fish at his high school. After the initial shock, he decided he likes being around smart people.
He’s having a great time and doing really well.
During the time I was at UCSD, the bottom 5% was "reserved" for the affirmative action admissions. Statistically, 85% of those students dropped out before graduation. It was a waste of taxpayer money. It was a waste of the time and money of the under qualified students. It was an injustice to the 5% of qualified students who were excluded to make room for the unqualified applicants.