What is the impact of managed care versus fee for service on overuse of carotid endarterectomy? The researchers examined the effectiveness of specific managed care interventions in reducing overuse. Specifically, the researchers addressed the following specific research questions: 1) Did Medicare beneficiaries enrolled in Medicare+Choice managed plans undergo carotid endarterectomy less often for inappropriate reasons compared with their counterparts in fee-for-service Medicare? 2) Compared with fee-for-service Medicare, did Medicare managed care enrollees receive carotid endarterectomy more frequently at high-volume hospitals or from high-volume surgeons? 3) Compared with fee-for-service Medicare, did Medicare managed care enrollees have carotid endarterectomy performed more frequently at hospitals or by surgeons with low risk-adjusted perioperative complication rates (i.e., at higher quality hospitals)? 4) What specific mechanisms for assessing appropriateness and quality did these plans use to prevent inappropriate carotid endarterectomies or to select providers with higher quality? What specific plan structural attributes, operational characteristics, or management programs are associated with lower (or higher) rates of inappropriate surgery? Which are associated with better (or worse) risk-adjusted complication rates? 5) Is there evidence of a managed care “spill-over effect” on quality of care such that appropriateness or complication rates are better among fee-for-service Medicare patients in regions with greater managed care market penetration than in regions with less managed care market share? The objective of the project was to inform the policy debate about what cost containment mechanisms may be effective in the current environment.