The center effect in kidney transplantation.

A "center effect," variability in outcome unrelated to case mix or chance, is a recognized determinant of outcome in kidney transplantation. Since earliest investigation, center size (volume) has been its primary surrogate. Transplantation has matured, and outcomes have progressively and uniformly improved, narrowing short-term differences between centers. Does the center effect still exist? And if so, what is its nature, beyond usual donor, transplant organ and recipient characteristics, which has been elusive?