Population health and clinical data linkage: the importance of a population registry

The Australian National Collaborative Research Infrastructure Strategy supports development of a national research capability in population health and clinical data linkage. This paper illustrates the importance of incorporating a population registry within such a system using an example provided by the Manitoba Injury Outcome Study (MIOS) that quantified the long-term burden of mortality attributable to injury in working-age adults.

MIOS is a population-based matched cohort study that used administrative health data from Manitoba, Canada. An inception cohort of injured cases (ICD-9-CM 800-995) aged 18-64 years was identified from all Manitoba hospital admissions between 1988 and 1991. A matched non-injured comparison group was randomly selected from the total provincial population using the Manitoba Population Registry. Mortality outcomes were obtained by linking the two cohorts with the deaths data over 10 years. Mortality rate ratios (MRRs) were calculated to compare the injured and non-injured cohorts.

A total of 21,032 matched pairs were identified. Using the population registry, the 10-year adjusted all-cause MRR comparing injured and non-injured cohort was 1.80 (95% CI 1.65-1.98). Without the registry, the unadjusted standardised morality ratio was 2.76 (95% CI 2.52-3.02).

The effect of injury on mortality outcomes was over-estimated using only the injured cases, without use of the population registry. Use of the population registry enabled the selection of a matched non-injured group for comparison purposes, ensured comprehensive follow-up of almost all participants, and provided more accurate estimates of exposure time, incidence of mortality and relative risk.