Methodological challenges of measuring primary care delivery to pediatric medicaid beneficiaries who use community health centers.

Efforts to measure quality of care have focused on ambulatory care providers. We examined the performance of community health centers serving children on Medicaid in 3 states. Descriptive analysis showed considerable patient population heterogeneity, and regression analysis demonstrated that variation explained by the assigned provider was small (mean R(2) = 4.3%) compared with the variation explained by patient demographic variables (mean R(2) = 29.9%). The results reinforce the need for caution when one is attributing quality differences to provider performance.