In the early 1970s, a group of researchers at the Washington University School of Medicine in St Louis, led by Robins and Guze , introduced a method that attempted to enhance the reliability as well as the validity of psychiatric diagnosis . For a limited number of diagnostic categories, the authors proposed research definitions that were based on clinical description, laboratory studies, exclusion of other diagnoses, follow-up studies and family studies. In addition, each category was defined by inclusion as well as exclusion criteria that were explicit, descriptive and either monothetic or polythetic. In the following years, the method was to be adopted not only for the definition of specific diseases, but for the definition of each category in psychiatric classifications.
The St Louis or Feighner definition of schizophrenia  rests upon three criteria: the presence of a chronic illness with at least 6 months of symptoms, in the absence of a period of depressive or manic symptoms sufficient to qualify for affective disorder; the presence of delusions or hallucinations or verbal production that makes communication difficult because of the lack of a logical or understandable organization; and at least three of the following manifestations: being single, poor premorbid social adjustment or work history, family history of schizophrenia, absence of alcoholism or drug abuse within one year of onset of psychosis, and onset of illness prior to age 40.
The St Louis criteria had a major influence on the development of other diagnostic criteria that have been elaborated over the years, in particular because all subsequent criteria sets have been moulded on the format of the initial St Louis criteria.
The Research Diagnostic Criteria (RDC)  were developed as part of a collaborative project on the psychobiology of depression that was sponsored by the National Institute of Mental Health (NIMH). The RDC provide explicit criteria for depressive disorders, schizophrenia and several other disorders.
The RDC for schizophrenia consist of a polythetic symptom criterion, a duration criterion and an exclusion criterion. The symptom criterion lists eight symptoms or groups of symptoms. The first seven symptom groups are
Schneiderian first-rank symptoms and other delusions or hallucinations, the last one gives diagnostic value to formal thought disorder if accompanied by either blunted or inappropriate affect, delusions or hallucinations of any type, or grossly disorganized behaviour. The duration criterion requires that signs of the illness have lasted at least 2 weeks from the onset of a noticeable change in the subject's usual condition, and the exclusion criterion describes the differential diagnosis with affective disorders: at no time during the active period of illness being considered did the subject meet the full criteria for either probable or definite manic or depressive syndrome to such a degree that it was a prominent part of the illness.
The RDC have been used extensively by researchers since they were first introduced and up to the present day. They may be applied on the basis of a comprehensive clinical examination or, preferably, a semi-structured interview, the Schedule for Affective Disorders and Schizophrenia (SADS) .
Over the years, a number of other explicit diagnostic criteria for schizophrenia have been developed by individual authors. Astrachan et al  have developed a schizophrenia index that attempts to define the concept of schizophrenia as proposed in DSM-II. Carpenter et al  have derived a flexible system for the diagnosis of schizophrenia, that was based on data from the International Pilot Study of Schizophrenia. Taylor and Abrams  have elaborated criteria that attempt to correct several aspects of the Feighner criteria. Pull et al  have produced diagnostic criteria that describe the concept of schizophrenia held by French psychiatrists until recently (Kellam . Berner et al  have developed the Vienna Research Criteria, based on the attributes of a fundamendal syndrome that the authors qualify as endogenomorphic-schizophrenic.
In the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III)  the method introduced by the St Louis group was first applied to define each of the disorders of a classification. The method was refined in the DSM-III-R  and DSM-IV  and was adopted in the research version of the ICD-10 .
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