Measurement of negative symptoms in schizophrenia.

This article focuses on the measurement of 'negative symptoms'. Standardized scales used to rate negative symptoms are reviewed and compared, as are the individual items which comprise them. The overlap of negative symptoms, akinesia, and depression is explored, and means are suggested to improve the precision of defining and measuring negative symptoms. Flat affect is the only item present in all negative symptom scales and may overlap with depression and akinesia. Inappropriate affect and attentional disturbance should not be considered negative symptoms. Poverty of speech and anhedonia lack unified definitions, and in some scales, they can also be confounded with depression and akinesia. The psychometric properties of most scales have not been sufficiently studied. The lack of long-term studies of stability of the supposedly enduring negative symptoms is especially worrisome. Carpenter's deficit syndrome consisting of non-secondary negative symptoms lasting more than one year is a promising new step to try and address some of these problems.