Characteristics of responding and nonresponding centers. (A) Distribution of transplantation volumes at responding and nonresponding centers. (B) Geographic distribution of responding and nonresponding centers. US regions: NEng indicates, New England; Mid-Atl, Mid-Atlantic; So-Atl, South Atlantic; ENC, East North Central; ESC, East South Central; WNC, West North Central; WSC, West South Central; Mt, Mountain; and Pac, Pacific.