Assessment of HCFA's 1992 Medicare hospital information report of mortality following admission for hip arthroplasty.

OBJECTIVE

The Health Care Financing Administration (HCFA) produced annually from 1987 through 1994 mortality data information as part of the Medicare Hospital Information Project (MHIP) report. We assessed the validity of these data for hip arthroplasty for one state Medicare population and we analyzed the accuracy of the predictions derived from the Bailey-Makeham mortality model for this procedure.

DATA SOURCES AND STUDY

SETTING

The study sample consisted of claims and model data from 1,421 Medicare patients who underwent hip arthroplasty at acute care Arkansas hospitals from October 1990 through September 1991.

STUDY

DESIGN

Patients were stratified into two groups based on reason for surgery (fracture status): reconstruction or fracture management. Patient survival experience was compared between the two groups. The effect of fracture status on the HCFA model's predictive ability was examined empirically and via a simulation study.

RESULTS

Our results indicate that hip arthroplasty patients are not uniform with regard to outcome, depending on the reason for the surgery. Patients with fracture had a much higher 30-day mortality rate than those who underwent reconstruction (p < .001). The empirical data and the simulation study suggest that the Bailey-Makeham model underestimates mortality for reconstructive surgery in fracture patients, providing a false benchmark for those institutions that perform hip arthroplasty on predominantly one category of patients.

CONCLUSION

Published HCFA data concerning mortality for hip arthroplasty combines two different patient populations into one statistic. Casual examination of these data could result in a false benchmark for analysis of institutional performance. An important implication from this study for policymakers who base decisions on "report cards" or performance measurement reports is that, although they are necessary,generic case-mix, comorbidity, and severity of illness adjustments may not be sufficient to achieve accurate representations of outcomes, and that more disease/procedure--specific adjustments may be needed to avoid inappropriate conclusions.