"Negative symptoms": conceptual and methodological problems.

Research into the so-called negative symptoms of schizophrenia is plagued by often ignored problems in item identification, scale selection, quantification, clinical assessment process, and symptom (and, probably, causal) nonspecificity. Neither a negative symptom syndrome per se nor the recent rating scales designed to measure it have been validated, although some data useful in this regard have been presented for the scales. Since no criterion against which to validate these scales exists, construct validation is needed. The construct of negative symptoms, as defined by its hypothesized empirical relationships with other variables, and the procedures used to measure it must be validated simultaneously and gradually through a programmatic series of studies. In the meantime, research results pertaining to negative symptoms should be interpreted with considerable caution.