Dimensional structure of psychotic symptoms: an item-level analysis of SAPS and SANS symptoms in psychotic disorders.

The factor structure of psychotic symptoms as assessed by means of the Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS) was examined in a sample of 660 psychotic inpatients. Analyses were conducted at item-level. Principal-component analysis (PCA) was used to extract factors, the OBLIMIN procedure to rotate factors, and the eigen value greater-than-one criterion to determine the number of factors. PCA resulted in 11 interpretable factors explaining 64% of the total variance: poverty of affect/speech, thought disorder/inappropriate affect, bizarre delusions, social dysfunction, other delusions, paranoid delusions, bizarre behavior, nonauditory hallucinations, auditory hallucinations, manic thought disorder, and attention. Many of the factors were significantly intercorrelated. A second-order PCA resulted in four second-order factors, the first three roughly corresponding to the well-known psychosis, disorganization and negative dimensions. It is concluded that the factor structure of psychotic symptoms is more complex than is generally acknowledged, and that the dimensions of psychosis, disorganization and negative represent second-order dimensions. The subscale composition of the SAPS and SANS was not supported.