"confounding factors. "<p>I'm going to go ahead and state the obvious. School systems (all social systems) filter for (relatively) functionally stable individuals. This is the case with the work-force too, and easily explains the correlation between the unemployed and the mentally ill. One does not cause the other, one filters out the other.<p>I guess it's easy to ignore this dark possibility; it would imply deep, and possibly irreparable facts of human nature.