Compare methods

	Relative Index of Inequality	Slope Index of Inequality
Field	Social Epidemiology	Social Epidemiology
Family	Regression model	Regression model
Year of origin	1997	1997
Originator	Anton E. Kunst & Johan P. Mackenbach; Jamie Sergeant & David Firth (estimation/inference)	Anton E. Kunst & Johan P. Mackenbach; Adam Wagstaff et al.
Type	Regression-based relative measure of health inequality across ordered SES groups	Regression-based absolute measure of health inequality across ordered SES groups
Seminal source	Mackenbach, J. P., & Kunst, A. E. (1997). Measuring the magnitude of socio-economic inequalities in health: an overview of available measures illustrated with two examples from Europe. Social Science & Medicine, 44(6), 757-771.	Mackenbach, J. P., & Kunst, A. E. (1997). Measuring the magnitude of socio-economic inequalities in health: an overview of available measures illustrated with two examples from Europe. Social Science & Medicine, 44(6), 757-771.
Aliases	RII, Relative Index, Kunst-Mackenbach Relative Index of Inequality, Relative Slope Index of Inequality	SII, Slope Index, Absolute Slope Index of Inequality, Kunst-Mackenbach Slope Index
Related	4	4
Summary	The relative index of inequality (RII) is the relative counterpart of the slope index of inequality: instead of the absolute difference in a health outcome between the bottom and top of the socioeconomic hierarchy, it expresses that difference as a ratio. Like the SII, it is built from a regression of the outcome on each group's position in the cumulative socioeconomic distribution, so it uses the whole population and accounts for group sizes rather than comparing only the extreme categories. Mackenbach and Kunst's 1997 overview recommended the RII alongside the SII as the standard pair of summary measures for socioeconomic health inequality, precisely because relative and absolute inequality can move in opposite directions and both need to be reported. Sergeant and Firth's 2006 Biostatistics paper clarified the various definitions of the RII, compared estimation strategies, and supplied a parametric bootstrap for valid confidence intervals. The RII is dimensionless, which makes it directly comparable across outcomes, time periods, and populations with very different baseline rates. It is a mainstay of comparative health-inequality research and routine surveillance.	The slope index of inequality (SII) is a regression-based summary measure that expresses the absolute difference in a health outcome between the bottom and the top of the socioeconomic hierarchy. Rather than comparing only the most extreme groups - which discards information and is sensitive to how categories are defined - it regresses the outcome on each group's relative position in the cumulative socioeconomic distribution and reads the inequality off the fitted line. Mackenbach and Kunst's 1997 Social Science & Medicine overview made the SII, together with its relative counterpart, the recommended pair of measures for quantifying socioeconomic inequalities in health because they use the whole population and account for group sizes. The SII is measured in the natural units of the outcome - extra deaths per 100,000, additional percentage points of disease prevalence - which makes it directly meaningful for public-health and policy audiences. Wagstaff, Paci, and van Doorslaer had earlier argued that such regression-on-rank measures, alongside the concentration index, are among the few that properly reflect the socioeconomic dimension of health. The SII has become a standard tool in health-inequality monitoring across Europe and beyond.