An international survey of tardive dyskinesia.

As part of an international study of chronic schizophrenia, data on tardive dyskinesia were collected by clinical judgment and a standard rating scale, on over 700 patients. The frequently-reported positive correlation between age and prevalence rate was confirmed in this sample. While not statistically significant, high prevalence rates were associated with higher dosage levels and length of hospitalization. Positive relationships were also found to exist among prevalence rates and schizophrenic subtypes--particularly among those with high degrees of negative symptomatology.