A multisite investigation of the reliability of the Scale for the Assessment of Negative Symptoms
Abstract
OBJECTIVE: The Scale for the Assessment of Negative Symptoms is a widely used instrument for measuring negative symptoms in schizophrenia, but few studies have examined its reliability. This study examined the interrater, internal, and test-retest reliabilities of the scale and its factor structure in the context of a multisite study. METHOD: Two hundred seven patients with schizophrenia who were participating in the Treatment Strategies in Schizophrenia study were assessed with the Scale for the Assessment of Negative Symptoms following a symptom exacerbation and again 3-6 months later. All assessments were performed by trained psychiatrists who were treating the patients. RESULTS: Interrater reliabilities ranged from low to high for the items on the Scale for the Assessment of Negative Symptoms but were statistically significant in most cases. Most correlations between individual items and subscale total scores were moderate to high, as were coefficient alphas for each subscale, indicating adequate internal consistency. Test-retest correlations were of moderate magnitude. Few differences in reliability statistics between sites were found, although differences in mean scale ratings between sites were present. A factor analysis indicated three factors corresponding to the Affective Flattening or Blunting subscale, the Avolition-Apathy and Anhedonia-Asociality subscales, and the Alogia and Inattention subscales. CONCLUSIONS: The results suggest that the Scale for the Assessment of Negative Symptoms has good reliability and is a useful instrument for the measurement of negative symptoms in multisite clinical studies. The internal reliability of the Alogia, Avolition- Apathy, and Inattention subscales could be improved by replacing some items and including additional items.
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