HIV Quality Report Cards: Impact of Case-mix adjustment and Statistical Methods
Methods: We used data from the Veterans Health Administration (VHA) HIV Clinical Case Registry and administrative databases to estimate case-mix adjusted viral control for local care systems in 2009. Patient-level viral control was defined as last HIV viral load measurement in year ≤ 400 copies/ml, among patients on potent antiretroviral therapy at least six months with at least two visits in year that were at least sixty days apart. Systems caring for > 25 eligible patients were included (patient N=12,368, system N=91). We compared system rankings created using two case-mix adjustment methods; the observed to expected estimator previsously used by the New York Cardiac Surgery Outcomes reporting system, and the risk-standardized ratio currently used by the Centers for Medicare and Medicaid Services (CMS) Hospital Compare program.
Results: Overall, 10,913 patients (88.2%) achieved viral control. Prior to case-mix adjustment, system-level viral control ranged from 51% to 100%. Seventeen (19%) systems were labeled as low outliers (performance significantly below the overall mean) and 11 (12%) as high outliers. Adjustment for case-mix (patient demographics, comorbidity, CD4 nadir, time on therapy, and income from VHA administrative databases) reduced the number of outliers by approximately one third, but results differed substantially by method. The adjustment model had moderate discrimination (c statistic = 0.66), suggesting potential for unadjusted risk when using administrative data to measure case-mix.
Conclusion: Case-mix adjustment strongly affects rankings of care systems on the viral control measure of HIV care quality. Given the sensitivity of rankings to selection of case-mix adjustment methods – and potential for unadjusted risk when using variables limited to current administrative databases – the HIV care community should explore optimal methods for case-mix adjustment before moving forward with public reporting.
K. Richardson, None
M. Schweizer, None
M. Vaughand-Sarrazin, None
E. Perencevich, None