Measuring comorbidity and overlap in the hospitalization cost for alcohol and drug abuse and mental illness.

This paper measures the cost of short-stay hospitalization in 1985 for alcohol and drug abuse and mental illness (ADM). We identify and quantify two measurement problems: comorbidity in which ADM disorders may play a secondary role to other diagnoses and "overlap" in which ADM disorders occur together. Using data from the National Hospital Discharge Survey, we estimate the ADM short-stay hospital costs to total $13.1 billion. Almost four-fifths are costs of care for patients with primary ADM diagnoses and the remaining one-fifth is attributed to ADM comorbidity. About one-fifth of both the ADM discharges and the days of care represent overlap for hospitalized patients.