Rating scales in research: the case of negative symptoms

Two measures of negative schizophrenic symptoms, the Scale for the Assessment of Negative Symptoms and the withdrawal-retardation subscale of the Brief Psychiatric Rating Scale, are found to be redundant when used together. Studies incorporating redundant measures have numerous disadvantages. Using multiple scales increases the cost and effort for the investigator, places a greater burden on research subjects, and compromises the interpretability of findings by increasing the probability of both Type I and Type II errors. A strategy for evaluating the use of multiple rating scales is suggested, and the theoretical basis of this strategy is discussed.