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The diagnosis of a "functional" psychiatric illness may be considered valid if the patients do not develop the features of a different illness, if they have a similar clinical course, and if an increased prevalence of the same disorder is encountered among their relatives. Diagnostic validity thus requires follow-up and family studies. Using these principles, the author summarizes his studies of hysteria and delineates the diagnostic criteria that have been appropriately validated.
Samuel B. Guzé (Sun,) studied this question.