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GLOSSARY
Disability-adjusted life years (DALYs).
A summary measure of population health status created for use by the World Health Organization (Murray and Lopez, 1996) to represent the global burden of disease in the form of lost years of healthy life due to either disability or premature death. The measure is constructed using expert-derived weights for the value of additional years of life at each age and weights for more than 100 categories of health deficits resulting from different diseases or injuries.
EQ-5D:
A five-dimension measure of health status developed by a consortium of European researchers using a mailed survey to collect information about health and functional states being experienced by individuals (EuroQol Group, 1990). Preference weights have been developed for the various health states described by the EQ-5D, making the measure suitable for use as quality adjustments to compute QALE.
Health-adjusted life expectancy (HALE):
A summary measure of population health that integrates morbidity and mortality by summing the products of expected years of life at each age by a numerical weight representing average health status at that age (Fryback, 1997). The units of HALE are health-adjusted life years (HALYs). The only established types of HALE measures use some direct or proxy quality-of-life adjustment that represents people’s preferences for different health states (see QALE).
Health-related quality of life (HRQL):
A class of measures of an individual’s overall health at a particular time that produces a single numerical summary of health-related quality of life on a scale anchored by 0 (state of being dead) and 1 (state of optimal health), with the property that the scale values specifically are constructed to represent degree or strength of preference for one health state over another. These weighting scales can form the morbidity component of a QALE measure.
Health status profile:
A multidimensional characterization of an individual’s health at a particular time that describes how healthy the person is relative to each dimension (e.g., having excellent perceived health). Examples include the Sickness Impact Profile (Bergner et al., 1981) and the SF-36 (the 36-item short-form of the Medical Outcomes Study survey created from the Rand General Health Survey (Brook et al., 1979). Such profiles are not preference-weighted and do not meet the requirements for health utilities measures but are widely used in observational and experimental studies.
Health Utilities Index (HUI):
Three health status indices (HUI:1, HUI:2, HUI:3) each an elaboration of its predecessor, developed by Canadian researchers (Wolfson, 1996). Weights for the HUIs were derived from population surveys using multiattribute utility theory preference elicitation techniques and have been used by researchers at Statistics Canada to compute population estimates of QALE. (The developers termed their resulting summary a “health-adjusted life expectancy,” but under the definitions here, the index qualifies as one of the subset of QALE measures.)
Mortality-based population health measure.
A measure of population health computed from information on deaths in a population without reference to morbidity. Examples include mortality rates (the number of deaths per 100,000 population, usually adjusted to a reference population age distribution) and population (average) life expectancy (expected duration of life averaged over all individuals and adjusted to a reference population age distribution).
Quality-adjusted life expectancy (QALE):
A category of HALE measures that represents people’s preferences for different health states, usually based on one of a specific class of measures of health-related quality of life (see HRQL). The units of a QALE are quality-adjusted life years (QALYs). For some purposes, including cost-effectiveness analysis, measures of health-related quality of life must be based on utilities or preferences for health states that meet the conditions of welfare economics, which assumes that individuals seek to maximize utilities (preferences for particular outcomes) and that overall societal welfare is some function of these individual utilities.
Quality of Well-Being (QWB) scale:
A well-established measure of health-related quality of life initially developed in the 1960s and 1970s for resource allocation and health planning purposes. It combines 23 general complexes of symptoms and problems with three domains of function (Kaplan et al., 1978). Preference weights for the different health states in this combined classification scheme were derived from a community-based psychometric survey. QWB weights have been used in the health policy literature and in the cost–utility analysis literature as the morbidity component of a QALE computation.
Summary measure of population health:
An integrative measure of population health that combines both mortality and morbidity data to represent overall population health in a single number.
Years of healthy life (YHL).
A measure created by the U.S. National Center for Health Statistics for use in the U.S. government report Healthy People 2000. YHL is computed using health state weights for 35 health status categories (combining self-rated health and level of activities of daily living function) and data from the National Health Interview Survey to adjust tables of U.S. life expectancy. The weights for health states were constructed to approximate health-related quality-of-life weights in the absence of primary data and explicit measures of health-related quality of life. The YHL is sometimes considered a quality-adjusted measure of population health status, but it does not meet the welfare economic assumptions described for health utility measures.
