Objective The factor-structure of schizophrenic symptoms has long been investigated by many investigators. Schizophrenia dimensions have been proposed as possible specific pharmacological targets. Some authors also advanced the hypothesis that dimensions, for specific dimensional profiles, could help to discriminate the heterogeneous schizophrenic-spectrum symptomatology as well as to identify homogeneous subgroups. Despite the advances in the knowledge of schizophrenia dimensions, only few dimensional models have been proposed, with few of them gaining awareness in clinical practice. Apart from the classical dichotomous positive-negative and a tridimensional positive-negative-disorganization models, further 4-factor and 5-factor models have been proposed. Despite these efforts there is still lack of consensus on the “real” schizophrenia dimensional structure. Moreover the degree to which a symptom could be considered dimension-specific is still debated. Aim of the study was to investigate the proposed dimensional structure of schizophrenia and the specificity of symptoms in a given dimension. Methods PubMed, Medline, and PsychInfo were searched online and key journals were searched manually for factor-analytic studies investigating the dimensional structure of schizophrenia. Papers were systematically reviewed. Studies conducted on patients who had schizophrenia, schizophreniform or schizoaffective disorder according to the DSM-IV, DSM-III or ICD-9 criteria were included. Multiple analyses in the same study were all included. A further analysis was conducted on factor-analytic studies using the Positive and Negative Syndrome Scale (PANSS) and with a 5-factor solution. Results Fifty-four factor analytic studies were found, the number of patients included was 13024 (55% outpatients). The studies identified 3 to 6 factors with a median of 5 factors. The mean total explained variance was 59.1 ± 9.5 (95% IC = 56.3-61.9). Ninety-nine studies using PANSS with a 5-factor solution were identified, including 4115 patients (Table II). Data are discussed herein. These findings suggest heterogeneity among factorial solutions in schizophrenia spectrum disorders. The structure and type of items of the rating scales might explain this heterogeneity. A 5-factor solution with “positive”, “negative”, “disorganization”, “excitement/hostility” and “anxiety-depression” seemed to adequately describe schizophrenic symptomatology in a heterogeneous group of patients (Figs. 1-5). However, few items (symptoms) seemed to be dimension-specific in this model. Conclusions Further studies with broad and valid psychometric instruments are needed to better clarify the dimensional structure of schizophrenia.
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