The ‘pseudopatient experiment’ was a field experiment carried out by David Rosenhahn and a group of seven other people between 1969 and 1972. The group of healthy, normal individuals all presented themselves at U.S. psychiatric hospitals, informing psychiatrists only that they were hearing a voice saying “empty”, “hollow” and “thud”. All of the patients were admitted to psychiatric wards, and all apart from one were diagnosed with schizophrenia. Even though the pseudopatients all behaved normally after being admitted, they were kept in the hospitals for an average of 19 days, and were administered medication.

Rosenhan DL (January 1973). “On being sane in insane places“. Science 179 (4070): 250–8