Neuroscientists and Cognitive Psychologist, What Are Some of the Concerns About Random Samples?

Psychologists and cognitive psychologists want a random sample. And having access to 9,000 or 30,000 people - they have to be computer users in order for this to work. But you know, almost everybody is now. It's not like you were doing a random sample of computer users 25 years ago,. which tended to skew towards a certain kind of person.