I have no idea. I would generally expect people to have more in common with others they meet at university than with others they meet in high school (more segregation by ability via university choice; more segregation by interests via subject choice) and to choose friends who are more likely to remain a good match in terms of personality, interests, etc. (people can change a lot between, say, age 16 and age 20) -- it's not just a matter of it being easier to lose touch with your high-school friends than with your university friends.