[The factor structure of schizophrenic symptoms: which model is supported by independent item analysis?]

Most studies that have investigated the symptom dimensions of schizophrenia utilizing the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS), both global rating scales, favored a 3-factor model. Only a few studies have examined the factor structure at the item level and they suggest a wider dimensional structure. The factor structure of schizophrenic symptoms has not been previously studied in Turkey, nor has the construct validity of these scales. The present study sought to determine the factor structure of the independent items and the construct validity of the scales.

The study included 180 schizophrenia patients (diagnoses based on DSM-IV criteria). The standard statistical methods of principal component analysis (PCA) and varimax rotation were used to extract factors.

PCA of the global items yielded a 3-factor solution, representing positive, negative, and disorganization dimensions. Item-level factor analysis revealed 12 factors: Psychomotor poverty, positive formal thought disorder, auditory/visual hallucinations, social and occupational dysfunction, bizarre delusions, attention/stereotypy, paranoid features, somatic hallucinations/delusions, appearance, grandiose/religious delusions, inappropriate affect, and delusions of jealousy.

Consistent with previous studies, neither the global nor the item-level factor structures supported the simple positive-negative dichotomy or the composition of the sub-scales; therefore, future studies should make use of the single items, especially when positive symptoms are being studied.