“We find that when students come to orientation, you know, before they start classes at Carolina. About half of the students say that they want to be biology majors and go to med school,” May said. “But what we know is biology graduates about 500 majors a year out of a class of 4,000. So that means something happens.”
So according to UNC’s data, 87.5% will change their major.
https://www.dailytarheel.com/search?a=1&o=date&ty=article&au=Jackson+Liu
ETA: The exact article won’t come up, but look for the title “UNC gives students opportunity to explore majors, but with it comes uncertainty” by Jackson Liu, 1/28/2018