In 1973, Rosenhan performed a study in which eight healthy adults were admitted to a psychiatric hospital. What did this study demonstrate?

During the Rosenhan experiment, eight healthy people checked themselves into mental hospitals and studied the conditions therein; below is a link to the actual study. Probably the most important finding of the study was that not a single one of the healthy adults was identified as such. Most of them were diagnosed with schizophrenia. This finding is interesting because it makes clear the possibility that there are no good ways in psychiatry for differentiating between someone who is healthy and someone who is mentally ill. 

A secondary finding was how mental health staff separated themselves from the patients; the higher the rank of a staff person, the less time that person spent with the patients. Psychiatrists spent the least amount of time and the attendants the most. Attendants spent as little time as they were allowed on the ward, preferring to stay behind the glass "cage" that separated staff from patients. 

Mental health is challenging to define, as Rosenhan's study demonstrates. Given the fact that a psychiatric diagnosis can be a stigma in a person's life, the fact that psychiatry cannot identify mentally healthy people means that there are people who have experienced the dehumanizing effects of the mental institution, the stigma of diagnosis, and the side effects of psychotropic drugs and who are not significantly ill, after all.