Elsevier

Social Science & Medicine

Volume 55, Issue 11, December 2002, Pages 1923-1928
Social Science & Medicine

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

https://doi.org/10.1016/S0277-9536(01)00321-5Get rights and content

Abstract

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.

Introduction

The measurement of income-related inequalities in health has become an important field in health economics (Wagstaff, Paci, & van Doorslaer, 1991). In a recent contribution, van Doorslaer et al. (1997) for instance used concentration indices to estimate income-related inequalities for nine industrialized countries using a measure of morbidity based on self assessed health. In a subsequent contribution, Gerdtham and Johannesson (2000) estimated concentration indices with respect to both measures of morbidity and health based on quality adjusted life years in different age groups in Sweden. They noted that the age pattern differed depending on whether the concentration indices were estimated with respect to morbidity or health. Recently, van Doorslaer and Koolman (2000) have found that ranking of relative inequality measures across countries depends on whether health or morbidity is used. To avoid this problem, they also report absolute inequality measures for each country. The main purpose of this methodological note is to illustrate why the ranking of relative income-related health inequality between countries and within countries across dimensions of health depends on whether inequality is measured with respect to health or morbidity. We also examine why this problem does not arise when absolute inequality measures are employed and exemplify these issues using comparisons of scales from the Short Form 36 (SF-36) (Ware & Gandek, 1998) included in population health surveys conducted in Sweden and Australia.

Section snippets

Methods

The last few years has witnessed the development of standardized surveys for measuring health status and these are likely to be increasingly used in the measurement and comparisons of health inequalities in different populations. A prime example is the SF-36 health survey that has been translated and studied in over 40 countries (Ware & Gandek, 1998). The SF-36 is a 36 item questionnaire that measures health in terms of eight multi-item scales: physical functioning (PF), role limitations due to

Results

Table 1 provides summary statistics for each scale of the SF-36 surveys by country. With the exception of BP the mean scores in the Swedish sample were significantly higher than those reported in the Australian sample. The concentration indexes for health scores by scale are reported in the second and third column of Table 2. In both Australia and Sweden, the highest degree of inequality was in RP with 0.033 and 0.031, respectively. The relative concentration indexes in terms of morbidity

Discussion

The concentration index has been used in comparisons of the income-related health inequality between countries (van Doorslaer et al., 1997). Our results show that whether the concentration index is defined with respect to morbidity or health can affect the ranking between countries and across dimensions of health. However, this issue is not confined to the concentration index as all relative health inequality measures (e.g. comparing the relative inequality of the highest and lowest income

Acknowledgements

We would like to thank Mark Dusheiko for helpful comments on a previous draft of this paper.

References (14)

There are more references available in the full text version of this article.

Cited by (0)

View full text