...and who on average have very limited life experience.

A random subset of psych majors is going to have very different characteristics than a random subset of dining hall student employees is going to have very different characteristics than a subset of frat members.

I can't vouch for this particular study, but my experience in college has been that possible differences between 'subset of psych majors' and the rest of the population are among the earliest considerations to, well, consider.