Very good point. That makes me question the validity of many, many psychological research studies that use college students as subjects. Not random, eh? Universities get grants, use their own students and then about 25% can be replicated.
$$$$$$
So many studies are just a bunch of cr@p; for example, 40 years ago the medical profession removed homosexuality from the list of mental illnesses for no other reason than political pressure. When the government first tried tracking the progress of AIDS, they quickly gave up when it became clear 1) how many sexual partners each homosexual had, and 2) how little they knew of their partners (since they favored sex with complete strangers). Absolutely nuts...