Summarizing Population Health: Directions for the Development and Application of Population Metrics

SUMMARY

Historically, policies to improve population health have focused on major causes of death such as smallpox and cholera. Policy priorities have, in turn, been guided by information on mortality and life expectancy, and governments and others have worked to collect comprehensive, reliable, and valid mortality data. As death rates have decreased and life spans have lengthened, however, people have become increasingly interested in other health goals such as preventing disability, improving functioning, and relieving pain and the distress caused by other physical and emotional symptoms. With broader goals, policymakers need additional information to help them make decisions and establish priorities for public health, biomedical research, and personal health services.

For some purposes and decisions such as making individual patient care decisions or reducing postoperative infection rates, detailed clinical, behavioral, and organizational information is required. For other purposes such as understanding broad trends in the public’s health or comparing the value of population health promotion strategies, it is helpful to have some overall picture or summary measure of health and well-being in addition to information on specific aspects or dimensions of health.

The development and application of summary measures of population health present complex and intriguing methodological, ethical, and political challenges. Methodologists have taken the lead in confronting these challenges, for example, in devising ways to summarize in a single measure the impact on population health of both mortality and morbidity. They generally have used one of several different methods to attach a single number—usually ranging between 0 (death) and 1 (optimal health)—to a complex of social and personal attributes that represent health status. This number has then been linked to life expectancy to form a single integrative measure of overall health. Under the overall measurement rubrics of health-adjusted life years (HALYs) or health-adjusted life expectancy (HALE), several kinds of measures have been developed. The best known include quality-adjusted life years (QALYs), years of healthy life (YHLs), and disability-adjusted life years (DALYs). Methodologists are still refining these measures to improve their reliability, validity, credibility, and ease of use.



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Summarizing Population Health: Directions for the Development and Application of Population Metrics SUMMARY Historically, policies to improve population health have focused on major causes of death such as smallpox and cholera. Policy priorities have, in turn, been guided by information on mortality and life expectancy, and governments and others have worked to collect comprehensive, reliable, and valid mortality data. As death rates have decreased and life spans have lengthened, however, people have become increasingly interested in other health goals such as preventing disability, improving functioning, and relieving pain and the distress caused by other physical and emotional symptoms. With broader goals, policymakers need additional information to help them make decisions and establish priorities for public health, biomedical research, and personal health services. For some purposes and decisions such as making individual patient care decisions or reducing postoperative infection rates, detailed clinical, behavioral, and organizational information is required. For other purposes such as understanding broad trends in the public’s health or comparing the value of population health promotion strategies, it is helpful to have some overall picture or summary measure of health and well-being in addition to information on specific aspects or dimensions of health. The development and application of summary measures of population health present complex and intriguing methodological, ethical, and political challenges. Methodologists have taken the lead in confronting these challenges, for example, in devising ways to summarize in a single measure the impact on population health of both mortality and morbidity. They generally have used one of several different methods to attach a single number—usually ranging between 0 (death) and 1 (optimal health)—to a complex of social and personal attributes that represent health status. This number has then been linked to life expectancy to form a single integrative measure of overall health. Under the overall measurement rubrics of health-adjusted life years (HALYs) or health-adjusted life expectancy (HALE), several kinds of measures have been developed. The best known include quality-adjusted life years (QALYs), years of healthy life (YHLs), and disability-adjusted life years (DALYs). Methodologists are still refining these measures to improve their reliability, validity, credibility, and ease of use.

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Important as methodological concerns and advances are, the ethical and policy implications of different measures and measurement strategies also deserve more systematic attention. In particular, alternative ways of valuing the duration of life, the quality of life, the burden of ill-health, or inequalities in health incorporate critical but not necessarily obvious or well-accepted judgments about whose life or what kind of life has meaning and worth. It is, therefore, important to examine—empirically and normatively—how the use of summary measures of population health can shape, improve, or distort decisions and how the analyses and resulting decisions compare to partial measures and to more traditional, often informal decisionmaking approaches. Much of the debate about summary measures is actually about policy choices that their use makes more explicit. Policymakers and policy analysts at all levels—international, national, regional, and local—would benefit from a better understanding of the strengths and limitations of different measures in informing decisions about how to invest limited resources to improve population health and well-being. This report from an Institute of Medicine (IOM) committee is intended to encourage methodologists, ethicists, and policymakers to learn from each other and to work together to identify the strengths, limitations, and appropriate uses of summary measures. In addition to the committee’s own expertise and experience, the report builds on discussions during a December 1997 workshop and the background papers (see appendixes) drafted for the workshop. The conclusions and recommendations that follow, each of which is discussed in more detail in subsequent sections of this report, describe directions for work to strengthen the credibility and utility of summary measures of population health. First, mortality measures, although important, provide decisionmakers incomplete and insensitive information about overall population health. Summary measures of population health need to recognize the physical and psychological illnesses and disabilities that cause much individual suffering and limit social and economic advances within and across nations. Second, summary measures of population health that integrate mortality and morbidity information are increasingly relevant to both public health and medical decisionmakers. Their actual and proposed uses include describing differences and trends in the health of populations; informing decisions about alternate uses of public health care dollars; and assessing the cost-effectiveness of alternative personal health care services and technologies. Third, the similarities and differences among summary measures of population health require further examination as part of a strategy for assessing how well particular measures and measurement strategies may serve different local, national, and international purposes. These assessments also need to include comparisons with simpler measures. Fourth, although methodological innovation in population metrics has strengthened the analytical base for health decisions, the lack of accepted standard measures often creates confusion and caution among potential users. Fifth, all measures of population health involve choices and value judgments in both their construction and their application. If these choices and judgments—and their policy implications—are not understood and acknowledged, the result can be distrust and disregard of the measures and those who promote their use. From these conclusions, the committee derived three recommendations. These recommendations, which are directed primarily at the U.S. Department of Health and Human Services