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. Author manuscript; available in PMC: 2010 May 1.
Published in final edited form as: Am J Kidney Dis. 2009 Apr 1;53(5):823–834. doi: 10.1053/j.ajkd.2008.12.040

Figure 1.

Figure 1

[EF5]Schematic representation of erythropoietin stimulating agent (ESA) responsiveness. Whereas the biological response of hemoglobin to ESA at individual HD patient level is positive longitudinally (responsiveness slope or β>0), at the population level in cross-sectional analyses the ESA responsiveness appears negative (β<0) due to the “confounding by medical indication”, i.e., individuals with higher hemoglobin levels tend to receive lower ESA dose, whereas those with lower ESA dose and worse ESA responsiveness receive higher ESA dose (see Technical Appendix for details).