The contribution of health plans and provider organizations to variations in measured plan quality.

Objective: Some argue that health plans have minimal impacts on quality of care and that quality data collection should focus only on physician organizations. We investigate the relative impact of physician organizations and health plans on quality measures.
Design: Statistical analysis of data on 9 Healthcare Effectiveness Data and Information Set (HEDIS) measures from 6 health plans and 159 provider organizations. We use regression analyses to examine the amount of variation in HEDIS measures accounted for by variation across provider organizations, and whether accounting for health plans explains additional variation. We also examine whether accounting for provider organizations explains away variation in HEDIS scores across health plans.
Setting: Six health plans and 159 contracted provider groups in California.
Main Outcome Measures: Nine HEDIS scores.
Results: For all nine measures studied, variation across provider organizations explains much of the HEDIS score variation. But, after accounting for variation across providers, variation across plans statistically significantly explains additional variation. We also find statistically significant differences across health plans in HEDIS rates that are not substantially affected when we control for the provider organization that cared for the patient.
Conclusions: On their face, these results suggest that plans can influence quality independent of the selection of physician organizations with which they contract, in contrast to hypotheses that plans are 'too far' from patients to have an influence. Continued attention to collecting plan-level data is warranted. Further work should address other possible sources of variations in HEDIS scores, such as variability in plan administrative databases.