Figure 4.

Geographic variation in market concentration is present in the United States. (A) Market competition index in 2001. (B) Market competition index in 2011. Note that variation in Herfindahl–Hirschman Index (HHI) is illustrated after creating five categories of HHI in increments of 0.2 and plotting the category of HHI for each hospital service area. Map includes the HHI for each hospital service area. Areas in white are where there were no patients receiving hemodialysis. Markets were least concentrated in the North East Census Region, the southeastern portion of the South Census Region, parts of Texas, the East North Central Census Division (i.e., Great Lakes region), and the Pacific Census Division.