Factor structure and clinical validity of competing models of positive symptoms in schizophrenia.

BACKGROUND

The factor structure of four competing models of positive symptoms and their clinical validity was studied in a sample of 253 schizophrenia inpatients.

METHODS

The following models were tested using confirmatory factor analysis: a one-dimension severity model, a two-dimension model comprising a psychosis factor and a disorganization factor, a four-dimension model based on the Scale for the Assessment of Positive Symptoms (SAPS) structure in subscales, and a five-dimension model derived from the previous one by further differentiating Schneiderian delusions from non-Schneiderian ones.

RESULTS

More complex multifactorial models fit the data better than simpler models. The five-dimension model was the best adjusted (goodness of fit index = .844, nonnormed fit index = .812, normed fit index = .728). Whereas the one-dimension model did not display significant association with the clinical variables, multidimensional models were related to age at onset and illness severity. The two-dimension model captured well the clinical correlates of the more complex models.

CONCLUSION

None of the tested models showed good fit to the data. The one-dimension model displayed both poor factor validity and poor external validity; therefore, research relying on the SAPS total score may reach misleading conclusions.