The purpose of the health care system is "to continually reduce the burden of illness, injury, and disability, and to improve the health and functioning of the people of the United States" (IOM 2001b). In the broadest sense, the performance of the health care system can be thought of as the degree to which this objective is met in actual practice, given current knowledge.

People legitimately hold widely different conceptions of what they consider to be the critical dimensions of health system performance. This kaleidoscope of views largely results from the perspective one adopts as a patient, physician, health care manager, purchaser, payer, or public health official or policymaker. The same health care encounter may be differently assessed depending on one's role—quality is in the eye of the beholder.

• A physician is likely to view performance in a technical sense, such as whether an accurate diagnosis is made, whether a surgical procedure is performed proficiently, and whether the patient's health status has improved.
• A patient is likely to judge an encounter with the health care system by its outcome in helping maintain or improve functioning and quality of life, and through a more personal lens, such as whether the physician listened well, communicated clearly, and was compassionate as well as skilled in delivering care.
• A health care manager, payer, or purchaser (including health plans, employers, and government programs such as Medicare and Medicaid) will want to know if the services are cost-effective: Was a desired health outcome achieved in the most efficient and effective manner? Employers also will be interested to know whether improving the quality of care increases the productivity of the workforce.
• A public health official or policymaker will wish to know whether health care resources are being put to their best use to optimize population health and whether services are being provided equitably within the population.

All of these perspectives are important to a well-balanced understanding of health system performance. Accordingly, the Institute of Medicine synthesized these perspectives into six related aims for the health care system: safe, effective, patient-centered, equitable, and efficient care that is accessible in a timely manner when needed (IOM 2001b, 2001c). These six domains are used to organize data on this Web site (see How to Use This Web Site).

Structure, Process, and Outcomes
Health care provision is often conceptualized in terms of cost, access, and quality. Quality, in turn, is often conceptualized in terms of its outcomes, processes, and structures (Donabedian 1980).

• Outcomes refer to the results of health care on the health of individuals and the population. Outcomes also include patient satisfaction with health care, which can influence willingness to seek care and adhere to treatment. For practical reasons, it is often necessary to measure proxy or intermediate outcomes such as preventable adverse events (hospitalizations for asthma), behavior changes (cessation of smoking), and risk factors for disease (control of high blood pressure).
• Process quality refers to the technical proficiency and interpersonal facets of interactions with patients. To improve quality, physicians need to know what processes of care—diagnosing, treating, and educating patients—are likely to achieve better outcomes under given circumstances. Measuring care processes that are linked to improved outcomes thus provides practical feedback to health care professionals and is often more feasible than measuring outcomes directly.
• Structural quality refers to the effect of health system attributes—such as the availability and types of health care providers and insurance—on the availability and provision of services. Accreditation programs measure certain organizational attributes that are believed to be important for providing high-quality care. Other surveys are beginning to measure attributes such as leadership, organizational culture, and information systems that have been associated with quality improvements (Ferlie and Shortell 2001).

The Institute of Medicine synthesized these concepts into the following widely cited definition: "Quality of health care is the degree to which health services for individuals and populations increase the likelihood of desired health outcomes and are consistent with current professional knowledge" (IOM 1990).