The need for operationalized criteria for the identification of schizophrenia is great. Schneider's diagnostic concept attempts the optimum in diagnostic clarity, using frequently occurring symptoms which can be reliably identified by various observers, and which he believes always indicate schizophrenia in the absence of an organic psychosyndrome. Schneider's approach, although never established by other investigators, is used for diagnosis throughout most of the world.
We found that the first-rank symptoms (FRSs) occurred frequently enough in acute schizophrenia to have diagnostic applicability. Individually, each FRS was found with greater frequency in schizophrenia. However, taken together, these symptoms which he considers pathognomonic of schizophrenia occur in one fourth of the cohort of manic-depressive patients. Therefore, Schneider's system for identifying schizophrenia, while highly discriminating, leads to significant diagnostic errors if FRSs are regarded as pathognomonic. Furthermore, FRSs did not have a postdictive or predictive function, as no relationship could be established between FRSs and duration or outcome of illness.