Within-center correlation in dialysis adequacy.

The purpose of this study was to determine whether patients with end stage renal disease treated with hemodialysis were correlated in dialysis adequacy within facilities. This was a retrospective analysis of dialysis adequacy based on urea reduction ratio (URR) values from 6969 patients dialyzed at 154 facilities. The within-center correlation was quantified using the between-center variation and the parameter p that was derived using ANOVA tables and mixed effects models. The variation in center means for URR was wider than expected for independent observations (52.9-76.1 versus 60.7-73.8, respectively). Furthermore, there was a significant within-center correlation in URR values across all facilities (p = 0.136, P<0.0001), which persisted after adjusting for patient specific covariates, facility characteristics, and state. In conclusion, there was a substantial within-center correlation in dialysis adequacy that reflected important center effects on the outcome of ESRD patients.