Communication disturbances in the natural speech of schizophrenic patients and non-schizophrenic parents of patients.

Subclinical communication disturbances in the relatives of schizophrenic patients appear to be heterogeneous in both form and origin. The Communication Disturbances Index (CDI) was applied to the natural speech of stable schizophrenic out patients, non-schizophrenic parents of patients, and control subjects. The parents of schizophrenic patients displayed more frequent overall instances of communication failure in their speech than the controls. The specific types of disturbance that were more frequent were structural lack of clarity, vague references and ambiguous word meanings. The parents did not differ significantly from the patients with regard to total CDI ratings. However, patients made more frequent missing-information references than parents, and parents made more frequent vague references than patients. High CDI scores in parents were associated with more severe lifetime core positive symptoms in their patient offspring.