This study investigates whether variation in Medicare Advantage plan performance on comprehensive diabetes care is explained by the case mix of plans. Using data on 513 Medicare Advantage plan-year observations for 2007 and 2008, the authors estimate multivariate regressions for 3 diabetes care quality measures: (1) hemoglobin screening, (2) low-density lipoprotein screening, and (3) retinal eye exam. Plan case mix is measured with the percentage of a plan’s enrollees who have type 1 diabetes with and without comorbidities and the percentage of a plan’s enrollees who have type 2 diabetes with and without comorbidities. Plans with a higher percentage of enrollees with type 1 diabetes with comorbidity and plans with a higher percentage of enrollees with type 2 diabetes without comorbidity have lower performance, on average. Finding evidence of a relationship between case mix and Healthcare Effectiveness Data and Information Set performance reinforces the argument for developing standardized risk adjustment or stratification methods in public reporting and pay-for-performance efforts.
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