Case-mix adjustment of the national CAHPS (R) benchmarking data 1.0: A violation of model assumptions?

Objective. To compare models for the case-mix adjustment of consumer report s and ratings of health care. Data Sources. The study used the Consumer Assessment of Health Plans (CAHPS (R)) survey 1.0 National CAMPS Benchmarking Database data from 54 commerci al and 31 Medicaid health plans from across the United States: 19,541 adult s (age greater than or equal to 18 years) in commercial plans and 8,813 adu lts in Medicaid plans responded regarding their own health care, and 9,871 Medicaid adults responded regarding the health care of their minor children . Study Design. Four case-mix models (no adjustment; self-rated health and ag e; health, age, and education; and health, age, education, and plan interac tions) were compared on 21 ratings and reports regarding health care for th ree populations (adults in commercial plans, adults in Medicaid plans, and children in Medicaid plans). The magnitude of case-mix adjustments, the eff ects of adjustments on plan rankings, and the homogeneity of these effects across plans were examined. Data Extraction. All ratings and reports were linearly transformed to a pos sible range of 0 to 100 for comparability. Principal Findings. Case-mix adjusters, especially self-rated health, have substantial effects, but these effects vary substantially from plan to plan , a violation of standard case-mix assumptions. Conclusion. Case-mix adjustment of CAMPS data needs to be re-examined, perh aps by using demographically stratified reporting or by developing better m easures of response bias.