Although "average'' health conditions at national and global levels may have improved, inequalities in health conditions still exist among and within countries (Mackenbach et al. 2008; Smits and Monden 2009). Epidemiologists often focus on average health and try to understand its determinants. This is important, but measuring and understanding inequalities in health, i.e. the gap in health between disadvantaged and better-off groups, is an additional concern for health policy makers, health communicators and health scientists.
Konings, P., Harper, S., Lynch, J., Hosseinpoor, A. R., Berkvens, D., Lorant, V., Geckova, A., & Speybroeck, N. (2010). Analysis of socioeconomic health inequalities using the concentration index. International Journal of Public Health, 55(1), 71-74. https://doi.org/10.1007/s00038-009-0078-y (Original work published 2010)