Health inequalities across socio-economic groups: Comparing geographic-area-based and individual-based indicators

Objectives: To compare health inequality estimates obtained with different types of indicators of socio-economic status (SES), and study whether some of these are better predictors of health status, as indicated by observed disability data, than others. Methods: Australian data were used to compare the use of the geographically based Socio-economic Index for Areas (SEIFA) in health inequality studies with two individual-based SES indicators able to account for family income and size. Inequalities in disability prevalences by SES were measured using age-standardized rate ratios. Logistic regression was used to determine which type of SES measure is a better predictor of the observed disability prevalences. Results: Estimates of health inequalities obtained with the SEIFA were considerably lower than those obtained with the individual-based SES indicators. With the SEIFA, the proportion of disabled people amongst the most disadvantaged 20% of Australians was estimated to be 82% higher than amongst the most advantaged 20%, compared with over 150% with the individual-based SES measures. Also, the individual-based indicators were considerably better predictors of observed disability status than the SEIFA. Conclusion: An individual-level SES indicator, such as one based on family income, is a better predictor of people with a disability than a geographic-area-based index. Also, the main reason for the considerably lower inequality estimates obtained with the SEIFA is that, unlike the individual-based indicators, such location-based indices cannot account for the significant, often age-related variations in SES that exist amongst people living in a particular area.