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

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. 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. 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. 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.