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The assessment of catatonic symptoms, unlike that of other schizophrenia symptoms, has not acquired accuracy and phenomenological rigour, and their distinction from extrapyramidal side-effects is not always easy. The Modified Rogers Scale can rate abnormalities in movement, volition, speech, and overall behaviour in schizophrenia. It is detailed, reliable and valid, and permits the isolation of a score for non-extrapyramidal and hence presumably catatonic phenomena.
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Lund et al. (1991) studied this question.
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