"He was called David Rosenhan and he devised a dramatic experiment. He assembled 8 people, including himself, none of whom had ever had any psychiatric problems.
Each person was sent across the country to a specific mental hospital. At an agreed time, they all presented themselves at their hospital and told the psychiatrist on duty they were hearing a voice in their head that said the word "Thud". That was the only lie they should tell otherwise they were to behave and respond completely normally."
David Rosenhan - "They were all diagnosed as insane and admitted to the hospital."
Question - "And were any of them insane?"
David Rosenhan - "No. There was nobody who could have judged these people as insane. ... but I told friends, I told my family, I get out when I get out; that's all. Be there for a couple of days and then I get out. Nobody knew I would be there for 2 months!"
They found there was nothing they could do to convince the doctors they were sane and it quickly became clear that the only way out would be to agree that they were insane and then pretend to be getting better.
Rosenhan agreed and after a month, the hospital proudly announced that they had discovered 41 fakes. Rosenhan then revealed that he had sent no-one to the hospital.
The effect of The Thud Experiment was a disaster for American psychiatry. It destroyed the idea that they were a privileged elite with specialist knowledge.