Validation of the Jarman's method of calculation of hospital standardised mortality ratios

[Truncated abstract] PURPOSE: The main purpose of this study was to evaluate the validity of Jarman-derived hospital standardised mortality ratios (HSMR) against Linkage-derived cumulative mortality ratios (CMR) in Western Australia. METHODS: Patients receiving inpatient care in Western Australia in 1980, 1985, 1990 and 1995 were identified as four single calendar year cohorts. Deaths reported on the basis of the ICD-9 classification were identified as those occurring during inpatient stay under the Jarman method and linked deaths occurring within 30 days of initial hospital admission under the Linked method. The latter were identified using the Western Australia Data Linkage System, which systematically links, within the State, all available administrative health data with regular updates. The System uses probabilistic matching of patient names and other partial identifiers to assign a project-specific, encrypted, individual identifier to maintain confidentiality. Under the Linked method, the System also allowed for the identification of inter-hospital transfers, thus enabling deaths within 30 days to be ascribed to the hospital of first admission, which was not necessarily the hospital in which a patient died. For both methods, observed numbers of hospital-related deaths were divided by the numbers expected on the basis of age and sex-specific mortality risks across the entire study population.