Psychometric analysis in support of shortening the Scale for the Assessment of Negative Symptoms.
Despite recent emphasis on the measurement and treatment of negative symptoms, studies of the Scale for the Assessment of Negative Symptoms (SANS) identify different symptom clusters, offer mixed support for its psychometric properties and suggest that it is shortened. The current study objective is to examine the psychometric properties of the SANS and the feasibility of a short research version of the SANS. Data were re-analyzed from three clinical trials that compared placebo and amisulpride to 60 days. Participants had chronic schizophrenia and predominantly negative symptoms (n=487). Baseline data were examined with exploratory factor analysis and Item Response Theory (IRT) to identify a short SANS. The short and original SANS were compared: with confirmatory factor analysis at endpoint; and on symptom response with mixed modeling to compare. Results showed that at baseline the SANS consisted of three factors labeled Affective-flattening, Asociality and Alogia-inattentiveness. IRT suggested a short SANSwith 11 items and 3 response options. Comparisons of the original and short SANS showed: the short version was a better fit to the data based on confirmatory factor analysis at endpoint; similar significant (p<.001) correlations between the baseline and subsequent scores; similar reliability; and similar significance (p<.05) on response based on mixed modeling. It is concluded that a short SANS is feasible to assess predominantly negative symptoms in chronic schizophrenia in research settings.