The Rosenhan experiment concluded that you cannot distinguish the sane from the insane in psychiatric hospitals. For those who aren't too familiar with the experiment, it took place in the early 1970s (1973, to be exact) and the specific psychologist was a guy by the name of David Rosenhan. Basically, for the first part of the experiment, he sent non-insane patients who briefly simulated auditory hallucinations and they were admitted to many different psychiatric hospitals in five different states (I think it was twelve hospitals.) They were diagnosed with psychiatric disorders and admitted to the hospitals. Then, once they were admitted, they acted normally and said that they felt fine. The staff at the hospitals didn't notice that, perchance, the "patients" might be normal and that they might be faking their psychiatric problems. They were all eventually released and they had to take antipsychotic drugs in order to be permitted to do so. These were normal people, mind you.
For the next part of the experiment, they asked doctors at some mental hospitals to detect "fake" patients. They hadn't sent any fake patients this time around, yet the doctors picked out many patients that they perceived as possibly being fake.
Back to what I said initially... this concluded that you can't tell the difference between a genuinely insane person and a normal person acting insane while you're in a psychiatric hospital. ^o^
Sorry for all the typing. I felt like sharing this; it's interesting to me, and may be interesting to at least a couple of you.