Dimensions of schizophrenic positive symptoms: an exploratory factor analysis investigation

Current psychopathology classifies schizophrenic positive symptoms into four groups: delusions, hallucinations, formal thought disorder, and catatonic symptoms. The present study explores the factor structure of different positive symptoms to refine this classification. The 35 positive symptoms of 429 psychiatric patients, consecutively admitted to any of 95 mental hospitals, with diagnosis of the ICD-10 F20 schizophrenia, were studied. After excluding those items with a base rate of 10% or less, factor analysis yielded six factors. The first factor was loaded by most of Schneider's first-rank symptoms and two specific auditory hallucinations; the second by all the catatonic symptoms and incoherence; the third by bodily delusions/hallucinations; the fourth by delusions of persecution and reference; the fifth by grandiose and religious delusions; and the sixth by visual and miscellaneous hallucinations. The finding that schizophrenic positive symptoms may have more than four dimensions suggests the need for reclassification of schizophrenic symptoms and for reconsideration of evidence-based diagnostic criteria for the disorder.