On the measurement of relative and absolute income-related health inequality

In recent work on international comparisons of income-related inequalities in health, the concentration index has been used as a measure of health inequality. A drawback of this measure is that it is sensitive to whether it is estimated with respect to health or morbidity. An alternative would be to use the generalized concentration index that is based on absolute rather than relative health differences. In this methodological paper, we explore the importance of the choice of health inequality measure by comparing the income-related inequality in health status and morbidity between Sweden and Australia. This involves estimating a concentration index and a generalized concentration index for the eight-scale health profile of the Short Form 36 (SF-36) health survey. We then transform the scores for each scale into a measure of morbidity and show that whether the concentration index is estimated with respect to health or morbidity has an impact on the results. The ranking between the two countries is reversed for two of the eight dimensions of SF-36 and within both countries the ranking across the eight SF-36 scales is also affected. However, this change in ranking does not occur when the generalized concentration index is compared and we conclude with the implications of these results for reporting comparisons of income-related health inequality in different populations.