It's really difficult working with kids and with babies because they are not cooperative subjects: they are not socialized into the idea that they should cheerfully and cooperatively give you information. They're not like undergraduates, who you can bribe with beer money or course credit.
Traditionally, psychology has been the study of two populations: university freshmen and white rats.
In brief, we do more research on men in prison, men in the military, and men in general than we do on women for the same reason we do more research on rats than we do on humans.
It is a failure of imagination and methodology to claim that it is necessary to experiment on millions of people without their consent in order to produce good data science.
I think something very simple that everybody can do is they can participate in medical research as subjects. Personal genome project, for example, will take on as many subjects as we can find.
Generally, we try to have a situation where the person is healthy, so you're not confounded by disease. So, that means that healthy individuals are donating their blood samples for the studies.
A spurious democracy has influenced both our research methods (I am sometimes tempted to define "validity" as part of the context of an experiment demanding so little in the way of esoteric gift that any number can play at it, provided they have taken a certain number of courses) and our research subjects (it would be deemed snobbish to investigate only the best people).
