"Nearly 50 percent of Americans have been mentally ill at some point 
in their lives, and more than a quarter have suffered from mental 
illness in the past twelve months. Madness, it seems, is rampant in America. "

"Science," he concludes "can tell us what has gone wrong with a 
person and which treatments will work best to fix it. But it cannot 
tell us whether we ought to treat a certain condition."

http://www.wired.com/wiredscience/2011/05/what-is-mental-illness-a-peek-through-the-murk/# 
review of Richard J. McNally's What is Mental Illness

www.peoplewho.org