Formal thought disorder, the type-token ratio and disturbed voluntary motor movement in schizophrenia.

Little work has been done to determine objective, reliable differences in formal characteristics of the actual utterances of thought-disordered and non-thought-disordered subjects. The type-token ratio (TTR), a quantitative measure of repetition in language, correlated highly with clinical judgments of thought disorder when spoken language was examined, and statistically differentiated thought-disordered from non-thought-disordered schizophrenics and psychiatric and normal controls. Elicited and spontaneous motor abnormalities were associated with reduced TTRs both in schizophrenics and in affective subjects with motor disturbance. The TTR is a reliable, objective indicator of language deviance and thought disorder, and strongly associated with motor disturbances.