VARIATION IN PRACTICE FOR DISCRETIONARY ADMISSIONS - IMPACT ON ESTIMATES OF QUALITY OF HOSPITAL-CARE

Objective.-To demonstrate theoretically and empirically the existence of systematic bias in commonly reported standardized hospital mortalit y ratios when variation in hospital admission practice is not adjusted for in the analysis. The underlying analytic model used in hospital m ortality analyses is specified and the confounding effect of selection bias arising from variation in admission practice is shown. Data Sour ces.-An empirical example is presented using state-level data from the Health Care Financing Administration's Medicare Hospital Information Report for 1988 to 1990. Study Selection.-The Medicare Hospital Inform ation data are used to demonstrate the effects of the bias because the y contain population-based admission rates and mortality rates. Data S ynthesis.-Selection bias arising from variation in admission practice causes the expected mortality rate to be overestimated for all hospita ls, but especially for hospitals with more lenient admission practices . Using the Medicare Hospital Information Report, the resulting standa rdized hospital mortality ratios are shown to be significantly inverse ly correlated with higher relative risks of hospitalization (P<.01). C onclusion.-Standardized hospital mortality ratios based on analyses th at do not account for Variation in admission practice among hospitals are biased. Variation in admission practice will cause any outcome mea sure based solely on hospitalized patients to be similarly biased. Cor rection for selection bias is required to produce valid measures of ho spital quality.