Method
Data
The study was approved by the Research Ethics Board of the Centre for Addiction and Mental Health in Toronto. We used California inpatient hospital admissions data from 1990 through 2000. The California Office of Statewide Health Planning and Development
(OSHPD) provided anonymized individual-level inpatient data collected from all California-licensed hospitals. The data set consisted of a record for each inpatient discharge from a licensed hospital (general acute care, acute psychiatric, chemical
dependency recovery, and psychiatric health facilities) but excluded federal hospitals. Each medical record can contain up to 25 diagnoses per hospital admission episode. Inpatient data were screened by the OSHPD’s automated data entry and reporting software program (MIRCal), and data fields with error rates of 0.1% or higher were returned to the hospitals for correction (8, 9). Reabstraction studies comparing OSHPD inpatient data files with original medical records found specificities for diagnoses ranging
from 0.98 to 1.00 and sensitivities for diagnoses ranging from 0.88 to 1.00 (8–10).