Factorial structure of the Scale of Prodromal Symptoms

Data from the Scale of Prodromal Symptoms (SOPS) [Early Intervention in Psychotic Disorders, pp. 135–150] on 94 hitherto never-psychotic individuals were entered into a principal components analysis, revealing six components with an eigenvalue greater than 1.0. Based upon scree-plot analysis, further extractions were limited to three, then two, factors. Varimax rotation of the three-component extraction revealed factors with reasonable congruence with a priori content areas. All symptoms labeled as negative in the SOPS loaded on one factor, and four of five symptoms labeled as positive loaded on another. The remaining positive symptom, conceptual disorganization, has been found not to load with other positive-labeled symptoms in studies of schizophrenia using applicable instruments. All symptoms labeled as “general” in the SOPS loaded on a third factor, which appears to reflect the nonspecific psychological distress that might be expected in psychosis-naı̈ve individuals experiencing the preliminary stages of a serious psychiatric disorder. The independence of this component from the positive and negative symptom factors suggests that the structure obtained suggests a clinical continuity between the at-risk presentations seen in this sample and established schizophrenia.