title: Excess mortality in small dialysis centers. The result of dialyzing high-risk patients.
abstract: End Stage Renal Disease Network 12 regularly collects information describing the Medicare dialysis population within its boundaries (Iowa, Nebraska, Missouri, and Kansas). Hoping to foster a regional quality improvement program, Network 12 began calculating provider specific mortality rates in 1988. These rates were extremely variable, but small dialysis units (< or = 30 patients) generally had higher mortality rates than their larger counterparts. To determine why mortality rates were inversely proportional to the number of patients treated within the center, we undertook a more intensive statistical review of patient mortality rate within the network. Actual and expected mortality rates were derived for each Network 12 dialysis center. Forty-eight percent of dialysis centers served 30 or fewer patients (small centers), and 40% had an expected mortality rate < or = 5 deaths per year. In 1989 and 1990, the crude mortality rate for dialysis centers enrolling 30 or fewer patients exceeded that of larger dialysis centers (p = 0.02). When Standardized Mortality Ratios were analyzed, this relationship disappeared (p = 0.83). Statistical review of dialysis providers is a complex process. Adjusting mortality rates for patient characteristics known to influence survival obviated the relation of dialysis unit size to patient mortality rate within Network 12. This suggests that patients were not randomly assigned to dialysis units and that small providers enrolled a disproportionate number of high risk patients. Adjusting mortality rates for endemic patient characteristics did not reduce the extreme variability noted in small mortality rates. This uncertainty, embedded in probability theory, cannot be eliminated from the statistical analysis of small samples.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medical Review Board of ESRD Network 12, Kansas City, Missouri, USA.
authors.forename: M
authors.initials: M
authors.lastname: Flanigan
mesh_terms: D006436:Hemodialysis Units, Hospital / Q000706:statistics & numerical data*; D006801:Humans; D007615:Kansas / Q000453:epidemiology; D007676:Kidney Failure, Chronic / Q000401:mortality* / Q000628:therapy; D008923:Missouri / Q000453:epidemiology; D009329:Nebraska / Q000453:epidemiology; D012044:Regression Analysis; D006435:Renal Dialysis / Q000401:mortality* / Q000592:standards; D015203:Reproducibility of Results; D018570:Risk Assessment