Dr. Shahram Yazdani Measuring Health Outcomes. Dr. Shahram Yazdani The measurement of health, in a...

Dr. Shahram Yazdani

Measuring Health Outcomes

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The measurement of health, in a way that is comparable over time and across populations, is an essential requirement for the evaluation of health policies, assessment of intervention effectiveness, and measurement of the efficiency of health systems.

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Definitions of Health

In 1941, Henry Sigerist, considering health in the context of human welfare, stated that “a healthy individual is a man who is well-balanced bodily and mentally, and well-adjusted to his physical and social environment.

He is in full control of his physical and mental faculties, can adapt to environmental changes, so long as they do not exceed normal limits, and contributes to the welfare of society according to his ability.

Health therefore is not simply the absence of disease; it is something positive, a joyful attitude towards life, and a cheerful acceptance of the responsibilities that life puts upon the individual”.

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Definitions of Health

This notion of health was endorsed by the President of the First World Health Assembly of WHO, Dr Andrija Stampar.

In this document, the founders of WHO famously defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.”

This definition was preceded by a declaration that “…the following principles are basic to the happiness, harmonious relations and security of all peoples” and followed by the statement that the “health of all peoples is fundamental to the attainment of peace and security…”.

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Health and Wellbeing

An important line of debate has revolved around the distinction between health and well-being.

In the 1970s and 1980s, a number of critics argued that health is a component of well-being, not identical to it, and that the WHO definition medicalized non-health elements of everyday life.

In attempts to define health more narrowly than well-being, two contrasting positions often have been adopted: the descriptivist and the normativist.

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Health and Wellbeing

The descriptivist argues that health and disease are concepts that can be specified in a value-neutral manner purely in terms of statistical deviation from typical levels of biological functioning, a position adopted by many bioethicists.

The normativist position, as elaborated by Nordenfelt, relates health to an individual’s ability to realize one’s vital goals. It thus makes health an inherently evaluative notion since an individual must achieve health in order to achieve happiness or well-being.

In this latter view, health is conceptualized in terms of integrated human functioning within a social context, and is culturally relative.

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Health State Valuation and Utility

Some health economists have explicitly defined health state valuations as measurements of the utility associated with health states.

However, utility has been defined somewhat circularly as the quantity that is maximized when individuals make choices that obey the axioms of expected utility theory, which offer a set of principles relating to preferences under uncertainty.

The use of the standard gamble technique for elicitation of valuations is linked to the axiomatic foundations of expected utility theory, but it is well appreciated that the standard gamble invokes both assessments of health levels associated with different states as well as attitudes towards risk and uncertainty.

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Health State Valuation and Utility

The notion of utility in the context of health state valuations conflates our concept of health with the separate concept of risk aversion, which we do not believe is relevant for characterizations of health levels in measures of individual or population health.

It is reasonable to assume that health state utility, as measured through the standard gamble, is related monotonically to the level of health, but responses to the standard gamble cannot be interpreted directly as quantifications of health levels.

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Health State Valuation and Quality of Life

The term quality of life (QoL) has been used widely in various social science contexts to refer to the overall, subjective appraisals of happiness or satisfaction experienced by individuals.

In this sense, it is a subjective notion, something “felt” or experienced, and should thus probably be distinguished from “goodness” or utility.

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Health State Valuation and Quality of Life

In health, the term QoL often has been used in a more particular way to refer to a multidimensional construct relating to symptoms, impairments, functional status, emotional states, and what we have labelled as health domains.

This use of QoL is clearly inconsistent with the general use of the term, so health researchers have taken to referring to this construct as “health-related QoL” (HRQoL).

To the extent that an individual’s HRQoL is conceived of as a vector of levels on “health-related” dimensions of life, it is similar to our conceptual framework for measuring health, albeit with less precisely articulated boundaries.

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Health Level

A health state valuation to provide a scalar cardinal index of the overall level of health associated with a multidimensional health state, defined in terms of a set of numbers quantifying capacity on each domain scale (e.g. level of mobility, level of self-care, level of affect, level of pain, and level of cognition).

In this conceptualization, health state valuations pertain strictly to the components of health, not to broader sets of components of well-being, or the contribution of health to well-being, or the felt sensation or satisfaction associated with a particular state of health.

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Health Level

One of the common elicitation techniques used in survey research on health state valuations is the time trade-off, which asks individuals to choose between different hypothetical scenarios that involve choices between improved health levels and reduced longevity.

On the face of it, this technique appears to parallel closely the notion of summary health measures that are based on equivalence between length of life and levels of health.

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Domains of health

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Domains of health in the WorldHealth Survey, 2002–2003

Mobility Self-care Pain and discomfort Cognition Interpersonal activities Vision Sleep and energy Affect

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Health Expectancies and Health Gaps

Summary measures of population health can be divided into two classes: health expectancies and health gaps.

These two classes of measures are in principle complementary

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Survivorship function for a population

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Health State Expectancies and Disability-Adjusted Life Expectancies

Health Expectancies: Those that use dichotomous health state

weights Disability-free life expectancy Life expectancy with disability

Those that use health state weights for a more disaggregated set of health states. Health-adjusted life expectancies Disability-adjusted life expectancy Healthy life expectancy

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Those that use health state weights for a more disaggregated set of health states. Health-adjusted life expectancies Disability-adjusted life expectancy Healthy life expectancy.

Disability-free life expectancy. This health expectancygives a weight of 1 to states of health with nodisability (above an explicit or implicit threshold)and a weight of 0 to states of health with any levelof disability above the threshold. Other examplesof this type of health expectancy include activelife expectancy, independent life expectancy, anddementia-free life expectancy.

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Life expectancy with disability. This is an exampleof a health expectancy which gives 0 weight to allstates of health apart from one specified state ofless than full health (in this case, disability abovea certain threshold of severity). Other examples of thistype of health expectancy include handicap expectancy,severe handicap expectancy, and unhealthylife expectancy.

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Health-adjusted life expectancies. These have beencalculated for Canada and Australia using populationsurvey data on the prevalence of disability atfour levels of severity together with more or lessarbitrary severity weights. Canada has alsoproduced the first estimates of health-adjusted lifeexpectancy based on population prevalence data forhealth states together with measured utility weights.

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Disability-adjusted life expectancy. This was calculatedfor the Global Burden of Disease Study usingdisability weights reflecting social preferences forseven severity levels of disability. DALE hasalso been calculated for Australia using prevalencedata from the Australian Burden of Disease Study and preference weights derived from the GlobalBurden of Disease Study and a Dutch study usingsimilar valuation methods.

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Healthy life expectancy. This has been calculatedby WHO for all 191 Member States for the years1999 through 2001 using methods that combineinformation from nationally representative populationsurveys and from the Global Burden of Disease2000 project, in order to maximize cross-populationcomparability.

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Macro- and micro-level summarymeasures of population’s health

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Defining The Outcome of Interest

The first use of GCEA is to compare a set of interrelated interventions, usually interrelated because they have the same goal—e.g. to reduce the risk of cardiovascular disease, or to improve the health of children under five years of age.

The second use is to provide information useful to the decision about how to allocate scarce resources from the perspective of the sector as a whole, which involves comparing the costs and outcomes of all the different types of health interventions that would be possible.

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This requires cost-effectiveness to be estimated using an outcome indicator which measures changes in health taking into account fatal and non-fatal outcomes.

Disability-adjusted life years (DALYs), healthy year equivalents (HYEs), or quality-adjusted life years (QALYs) are all time-based measures of health that include the impact of interventions on years of life lost due to premature mortality and years of life lived with a non-fatal health outcome, weighted by the severity of that outcome.

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WHO-CHOICE employs DALYs in its CEA, and we recommend that other analysts also use DALYs in any GCEA for purposes of comparability.

The metric has become increasingly used in the cost-effectiveness literature

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Disability-Adjusted Life Years (DALYS)

DALYs were first used in The Global Burden of Disease and Injury (GBD) study, a joint study between the World Bank, the World Health Organization (WHO) and Harvard School of Public Health.

This study began in 1988 with the objective to quantify the burden of disease and injury of human populations and define the main health challenges at the global level using a measure that could also be used for cost-effectiveness analysis.

Using DALYs, the GBD was measured for 1990 and projections were developed to 2020.

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Estimates of disease burden were combined with estimates of cost-effectiveness using DALYs in The World Development Report of 1993 in order to define priorities for investments in health.

This summary measure of population health has since been refined and is used routinely by WHO for reporting on the health of populations and as an outcome measure for CEA

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The DALY extends the concept of potential years of life lost due to premature death (PYLL) to include equivalent years of “healthy” life lost by virtue of being in states other than good health.

DALYs lost due to a disease or health condition are calculated as the sum of the years of life lost due to premature mortality (YLL) in the population and the equivalent “healthy” years lost due to non-fatal health conditions (YLD):

DALY = YLL + YLD

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The loss of healthy life due to non-fatal health conditions (YLD) requires estimation of the incidence of the health condition (disease or injury) in a specified time period.

For each new case, the number of years of healthy life lost is obtained by multiplying the average duration of the condition (to remission or death) by a severity weight that measures the valuation of the loss of healthy life.

Time lost due to premature mortality (YLL) is a function of the death rate and the duration of life lost due to a death at each age.

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Non-fatal Health Outcomes

In order to use time as a common currency for non-fatal health states and for years of life lost due to mortality, it is necessary to define, measure and numerically value time lived in non-fatal health states.

The “valuation” of time lived in non-fatal health states formalizes and quantifies social perceptions of how time lived in a particular state compares with full health.

Depending on how these valuations are derived and in which summary measure they are used, they have variously been called disability weights, health state valuations, health state preferences or health state utilities.

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When measuring the burden of disease, or the decrement in health due to a disease or condition, each year of life lost is given a weight of 1.

Years lived, but in states less than full health, are given a weight between 0 and 1, with 0 representing full health.

While death is not difficult to define, non-fatal health states are. Nonfatal outcomes of disease differ in their impact on the individual, and the impact on the individual is mediated by contextual factors including personal characteristics and the physical and social environment.

Nonfatal outcomes involve multiple domains such as mobility, anxiety and pain: health state valuations provide the means to weight and then aggregate individual functioning on these domains of health.

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The health state valuations used to estimate the burden of disease in terms of DALYs lost do not represent the lived experience of any disability or health state, or imply any societal value of the person in a disability or health state.

Rather they quantify societal preferences for health states in relation to the societal “ideal” of good health.

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Thus a weight for paraplegia of 0.57 mean that on average, society judges a year lived with paraplegia (weight 0.57) as less preferable than a year lived in full health, and a year with paraplegia is less preferable to a year with blindness (weight 0.43).

In addition, society would prefer a person to live three years with paraplegia followed by death than have one year of good health followed by death (3 years x (1-0.57) = 1.3 “healthy” life years is greater than 1 year of good health).

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Other things being equal, society would prefer to prevent or cure a case of paraplegia (weight 0.57) rather than a case of low back pain (weight 0.06), if each could be restored to full function for the same cost and there were insufficient resources to do both.

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DALYs and CEA

For CEA, the denominator is the gain in health due to an intervention rather than the loss measured in burden of disease (BOD) calculations.

Even though the same metric is used, the DALY is a negative concept in BOD calculations (DALYs lost) and a positive concept in CEA (DALYs averted).

For that reason, the valuations used in CEA calculations are the complements (e.g. 1-health decrement) of the weights used in BOD analysis.

For CEA, full health is valued at 1, with 0 representing the worse possible state of health, in this case death.

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Thank You !

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