To create rating of Californias nine largest commercial HMOs using clinical quality data from the Healthcare Effectiveness Data and Information Set (HEDIS) and member satisfaction data from the Consumer Assessment of Healthcare Providers and Systems (CAHPS) survey, the purpose of which is to provide the public (consumers, purchasers, advocates, regulators, and the industry) with useful and usable information on the quality of California health care across all aspects of the health care system.