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Calculating the concentration index when income is grouped

  • Clarke, Philip
  • Van Ourti, Tom

The problem introduced by grouping income data when measuring socioeconomic inequalities in health (and health care) has been highlighted in a recent study in this journal. We re-examine this issue and show there is a tendency to underestimate the concentration index at an increasing rate when lowering the number of income categories. This tendency arises due to a form of measurement error and we propose two correction methods. Firstly, the use of instrumental variables (IV) can reduce the error within income categories. Secondly, through a simple formula for correction that is based only on the number of groups. We find that the simple correction formula reduces the impact of grouping and always outperforms the IV approach. Use of this correction can substantially improve comparisons of the concentration index both across countries and across time.

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Article provided by Elsevier in its journal Journal of Health Economics.

Volume (Year): 29 (2010)
Issue (Month): 1 (January)
Pages: 151-157

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Handle: RePEc:eee:jhecon:v:29:y:2010:i:1:p:151-157
Contact details of provider: Web page: http://www.elsevier.com/locate/inca/505560

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  1. Wagstaff, Adam, 2002. "Inequality aversion, health inequalities, and health achievement," Policy Research Working Paper Series 2765, The World Bank.
  2. Erreygers, Guido, 2009. "Correcting the Concentration Index: A reply to Wagstaff," Journal of Health Economics, Elsevier, vol. 28(2), pages 521-524, March.
  3. Kakwani, Nanak & Wagstaff, Adam & van Doorslaer, Eddy, 1997. "Socioeconomic inequalities in health: Measurement, computation, and statistical inference," Journal of Econometrics, Elsevier, vol. 77(1), pages 87-103, March.
  4. Humphries, K.H. & Van Doorslaer, E., 1998. "Income-Related Health Inequality in Canada," Centre for Health Services and Policy Research 98:10d, University of British Columbia - Centre for Health Services and Policy Research..
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  7. Philip Clarke & Tom Van Ourti, 2009. "Correcting the Bias in the Concentration Index when Income is Grouped," CEPR Discussion Papers 599, Centre for Economic Policy Research, Research School of Economics, Australian National University.
  8. van Doorslaer, Eddy & Wagstaff, Adam & van der Burg, Hattem & Christiansen, Terkel & De Graeve, Diana & Duchesne, Inge & Gerdtham, Ulf-G & Gerfin, Michael & Geurts, Jose & Gross, Lorna, 2000. "Equity in the delivery of health care in Europe and the US," Journal of Health Economics, Elsevier, vol. 19(5), pages 553-583, September.
  9. Wagstaff, Adam & van Doorslaer, Eddy, 2000. "Chapter 34 Equity in health care finance and delivery," Handbook of Health Economics, in: A. J. Culyer & J. P. Newhouse (ed.), Handbook of Health Economics, edition 1, volume 1, chapter 34, pages 1803-1862 Elsevier.
  10. Hansen, Lars Peter, 1982. "Large Sample Properties of Generalized Method of Moments Estimators," Econometrica, Econometric Society, vol. 50(4), pages 1029-54, July.
  11. Tom Van Ourti, 2004. "Measuring horizontal inequity in Belgian health care using a Gaussian random effects two part count data model," Health Economics, John Wiley & Sons, Ltd., vol. 13(7), pages 705-724.
  12. Rasche, R H, et al, 1980. "Functional Forms for Estimating the Lorenz Curve: Comment," Econometrica, Econometric Society, vol. 48(4), pages 1061-62, May.
  13. Wagstaff, Adam & Paci, Pierella & van Doorslaer, Eddy, 1991. "On the measurement of inequalities in health," Social Science & Medicine, Elsevier, vol. 33(5), pages 545-557, January.
  14. Adam Wagstaff & Eddy van Doorslaer, 2004. "Overall versus socioeconomic health inequality: a measurement framework and two empirical illustrations," Health Economics, John Wiley & Sons, Ltd., vol. 13(3), pages 297-301.
  15. Erreygers, Guido, 2009. "Correcting the Concentration Index," Journal of Health Economics, Elsevier, vol. 28(2), pages 504-515, March.
  16. Adam Wagstaff, 2005. "The bounds of the concentration index when the variable of interest is binary, with an application to immunization inequality," Health Economics, John Wiley & Sons, Ltd., vol. 14(4), pages 429-432.
  17. Doorslaer, Eddy van & Jones, Andrew M., 2003. "Inequalities in self-reported health: validation of a new approach to measurement," Journal of Health Economics, Elsevier, vol. 22(1), pages 61-87, January.
  18. Meheus, Filip & Van Doorslaer, Eddy, 2008. "Achieving better measles immunization in developing countries: does higher coverage imply lower inequality?," Social Science & Medicine, Elsevier, vol. 66(8), pages 1709-1718, April.
  19. Chen, Zhuo & Roy, Kakoli, 2009. "Calculating concentration index with repetitive values of indicators of economic welfare," Journal of Health Economics, Elsevier, vol. 28(1), pages 169-175, January.
  20. Tom Van Ourti & Philip Clarke, 2011. "A Simple Correction to Remove the Bias of the Gini Coefficient due to Grouping," The Review of Economics and Statistics, MIT Press, vol. 93(3), pages 982-994, August.
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