Figure 2.

Despite wide geographic variation at any point in time, an index of market concentration was unchanged over time, while the number of choices available to patients increased slightly. (A) Number of dialysis facility choices. (B) Market concentration index. Increases in the number of competing providers from which patients could choose occurred gradually, whereas the distribution of an index of market concentration remained stable over the decade. Note that vertical bars indicate 10th and 90th percentiles. Boxes represents 25th and 75th percentiles. Middle bars represent median Herfindahl–Hirschman Indices (HHIs) and number of choices. Illustrated distributions are weighted by the number of patients in each hospital service area.