Rosenhan's study consisted of two parts. The first involved the use of healthy associates or 'pseudopatients', who briefly simulated auditory hallucinations in an attempt to gain admission to 12 different psychiatric hospitals in 5 different states in various locations in the United States. The second involved asking staff at a psychiatric hospital to detect non-existent 'fake' patients. In the first case hospital staff failed to detect a single pseudopatient, in the second the staff falsely detected large numbers of genuine patients as impostors. The study is considered an important and influential criticism of psychiatric diagnosis.