The Conceptual Basis for Measuring and Reporting on Health

The conceptual basis for measuring and reporting on health

Somnath Chatterji Bedirhan L Ustün Ritu Sadana Joshua A Salomon Colin D Mathers Christopher JL Murray

Global Programme on Evidence for Health Policy Discussion Paper No. 45

World Health Organization 2002

I. BACKGROUND

In 1941 Henry Sigerist, analysing the relevance of health for 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.” (1)

This was endorsed by the President of the First World Health Assembly of WHO, Dr Andrija Stampar from the School of Public Health in Zagreb, who played a crucial role in drafting the definition of health that was to be incorporated into the first paragraph of the preamble to the WHO Constitution and subsequently into the International Covenant on Economic, Social and Cultural Rights.

Thus, the founders of the World Health Organization defined health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity”. The introductory sentence preceding the above definition in the constitution stated “…the following principles are basic to the happiness, harmonious relations and security of all peoples”. The constitution further went on to say “The health of all peoples is fundamental to the attainment of peace and security…” (2).

This definition drew attention to health states rather than to categories of disease or mortality and placed health in a rather broad context of human well-being in general. However, this definition: • equates health with three domains of overall well-being • views health as a prerequisite for full well-being, and thus is perhaps more an ideal to aspire to, rather than a description of a state. • is not sufficient to develop operational indicators of health.

Our characterization of health ought to be consistent with basic consensus points about the nature of health, or else what we end up characterizing, though potentially both operationalized and measurable, may not be health in any ordinary sense: based on the intuitive understanding of health that most societies have. That some core notion of health exists across populations despite socio-cultural variation on the determinants and experience of health, is consistent with current thinking on common values (3). This is more than a matter of face validity, although that is certainly important. It is also an implicit obligation that WHO is under to fashion its mandate in terms of a characterization of health that is in alignment with the common understanding of health around the world.

Three consensus points about health are basic components of face validity: i) that health is a separate concept from well-being, and is of intrinsic value to human beings as well as being instrumental for well-being; ii) that health is comprised of states or conditions of the human body and mind and therefore any attempts to measure must include measures of body and mind function; and

2 iii) that health is an attribute of an individual person though aggregate measures of health may be used describe populations or aggregates of individuals.

During the last three decades, there has been general acceptance of an approach to describing health states of individuals in terms of multiple domains of health, and in developing self- report instruments that seek information on each of these domains (4–10). Although most of these previous measurement efforts were lead by researchers in North America and Europe, within other regions similar approaches are now underway1.A health state is thus a multidimensional attribute of an individual that reflects his or her levels on the various components or domains of health. Thus, a health state differs from pathology, risk factors or etiology, and from health service encounters or interventions.

How to describe health states is a central challenge in undertaking the measurement of health. What is the relationship of health states to other aspects of health such as risk of future health states or risk of mortality. In the following section, we describe three approaches to a complete characterisation of health before returning to the issue of describing and measuring health states.

II. COMPARING INDIVIDUAL HEALTH: WHAT TIME PERSPECTIVE?

When comparing or measuring individual health, the key question often asked “Is person A healthier than person B?” When answering this question, different time perspectives may be adopted: health state at a moment in time, health over the entire lifespan, or current and future health (11).

Figure 1. Current health for A and B

100 90 80 A 70 60 Sports injury 50 B 40

% full health 30 Road traffic injury - multiple 20 broken bones 10 0 0 20406080100 Age (years)

1 In fact, WHO has stimulated the creation of networks and research specifically to investigate conceptual and measurement approaches to health that reflect viewpoints from all regions of the world.

3 II.1 Current health One perspective on answering this question is to focus narrowly on health as it right now. Using this perspective, the individual in the state with the highest level of health, is healthier – ignored are any differences in future risks of adverse health outcomes or mortality. Figure 1 shows such a snapshot view: person A is healthier than person B (we defer until Section VI the issue of placing a single numerical value on a state of health). This approach is often used to compare individuals with relatively acute conditions, and is similar to a period measure within demography or epidemiology.

II.2 Lifetime health In contrast, an alternative perspective taken when answering this question is to compare health states that person A and person B experienced over their entire lifetime. Here the response is much more broader as it takes into account acute and chronic health states (non- fatal) as well as mortality (fatal). From this lifetime perspective, the individual that lived the most years of healthy life would be healthier. Figures 2 and 3 illustrate the lifetime health for person A and person B: even though both lived the same number of years, person A’s lifetime was healthier than person B’s.

Figure 2. Lifetime Health for person A Figure 3. Lifetime Health for person B

100 100 90 90 Diabetes 80 80 70 70 Measles Sports 60 injury 60 50 50 40 40 Depression Alzheimer's % full health % full health % full 30 30 Road traffic 20 20 accident 10 10 0 0 0 20 40 60 80 100 0 20406080100 Age (years) Age (years)

Although comprehensive, this perspective requires following individuals over the course of their lifetime until death before comparisons may be made.

II.3 Current Health and Future Prospects A third perspective taken when answering this question accounts for both the current state of health and prospects for survival and future health states. This perspective is closest to a common sense notion of whether one individual is healthier than another. In this view, the past remains excluded, but the influence of the past on current or future health is captured. The comparison of individual health is thus based on each individual’s health expectancy - the expectation of years of healthy life. This may depend on various risk factors, for example, genetic and environmental factors, other risk factors, information on lifestyles, and disease or illness trajectories (e.g. duration, remission, latent period, case-fatality) as well as on current health state.

These perspectives concern the comparison of individual health, but may also be relevant to the comparison of population health.

4 II.4 Measurement Challenge In order to measure and report on the health of populations or individuals, under any of the three views outlined above, it is necessary to develop a valid, reliable and comparable way to measure health status. This requires the following:

• a classification of health state domains • specification of a set of domains necessary and sufficient to describe health states for measurement purposes; • specification of what we are measuring in each domain; • a common understanding of what is full health versus exceptional talent in any given domain; • and, if we wish to construct summary measures of average level of population health, a method to place a single cardinal value on the overall level of health associated with a health state defined on multiple domains.

We examine each of these issues in the following sections and outline an operationalizable approach to the measurement of health states.

III. THE WHO FRAMEWORK FOR HEALTH CLASSIFICATION

III.1 The International Classification of Diseases The International Classification of Diseases and Related Health Problems (ICD) was developed by the WHO as a means of classifying causes of mortality and has since grown to be a diagnostic system for health conditions (12). It is the result of an effort to create a universal diagnostic system that began at an international statistical congress in 1891 with an agreement to prepare the causes of death for common international use. Subsequently revisions took place every 10 years. In 1948 when the World Health Organization was formed the 6th revision of the ICD was produced. Member states since then undertake to use the ICD in their national statistics.

The purpose of the ICD is to permit the systematic recording, analysis, interpretation and comparison of mortality and morbidity data collected in different places and at different times. In practice, the ICD has become the international standard diagnostic classification for all general epidemiological purposes. These include the analysis of the general health situation of population groups and the monitoring of the incidence and prevalence of diseases and other health problems in relation to other variables.

The ICD can be used to classify diseases and other health problems. As noted above, though, its original use was to classify causes of mortality as recorded at the registration of death, later its scope was extended to include diagnoses and causes of morbidity. In addition, the ICD also provides for a wide variety of signs, symptoms, abnormal findings, complaints, and social circumstances that may be reasons for contact with a health service that may not qualify for a formal diagnosis. It can therefore be used to classify data such as "diagnosis", "reason for admission", "conditions treated" and "reason for consultation", from which statistics and other health-situation information can then be derived. Further, five special tabulation lists are recommended for international comparisons and publications: four for mortality and one for morbidity.

5 III.2 The International Classification of Functioning, Disability and Health (ICF)

Over the last three decades or so there has been a gradual shift in thinking about health conditions. Increasingly it has become clear that diagnosis and causes and extent of mortality do not tell us very much about the impact of health conditions, the utilisation of resources and the need for services. Hence, the focus has gradually shifted from diagnostic descriptions alone towards understanding health conditions in terms of disabilities, functioning and health states. Functioning is the level of capacity or performance in any domain of health while disability is any decrement from a specified norm.

The World Health Organization, in recognition of this need, published the International Classification of Impairments, Disabilities and Handicaps (ICIDH) in 1980 to provide a framework for the study of disablement (13). Since its publication nearly two decades ago the ICIDH has been extensively used across the world and translated into several languages internationally. Over these years advances in disability-related research suggested the need for a revision of the ICIDH framework in order to provide a more coherent and comprehensive classification of health and disability states.

The second version of the ICIDH, now called the International Classification of Functioning, Disability and Health or ICF (14) consists of two major components that can be used to describe health states: at the level of the body it groups body functions and structures according to different body systems and at the level of the person and society it groups various domains of activity and participation. The ICF replaces the ICIDH concepts of disability and handicap by the concepts of capacity and performance and applies these constructs to a single list of activity and participation domains (tasks or actions).

Capacity refers to an individual’s ability to execute a task or action in a uniform facilitating environment assuming motivation to perform the task eg. the individual’s ability to walk 100 metres on a level well lit non-slippery surface. Performance describes whether an individual performs the task or action in his or her current environment. Thus the gap between current capacity and performance reflects the impact of the actual environment (and perhaps motivation) relative to the uniform environment. Both performance and capacity may be measured either with or without an individual’s personal aids.

The ICF is the result of an extensive revision process involving empirical field testing, expert consultations and endorsement of constituencies of health statisticians as well as disabled peoples’ organizations. In conjunction with the ICD it now forms the WHO family of international classifications and together they can be used to classify health states and their disease and injury causes.

IV. WHAT DOMAINS SHOULD WE INCLUDE IN HEALTH?

The WHO definition of health notes that health is a multi-dimensional concept. There are potentially three sets of domains that can be specified in order to describe health and contribute to a health state description: • core domains of health that almost all people agree upon as important to the direct measurement of health • additional domains of health that most people agree are direct measures of health, but that might not provide important information additional to the core domains

6 • other domains that are related to health and serve as good proximate measures of the experience of health – those that are indirect measures of health. Potential domains in each of these three categories are illustrated in Figure 4, based on an extensive review of existing health state measurement instruments and health measurement literature (15). The items in bold are proposed as the core domains that almost all people agree upon. The distinction between domains that directly measure health and those that indirectly measure health, e.g., health-related domains, is discussed further in Section V.

Figure 4. Domains of Health

Direct measures of Health: Vision Hearing Affect Pain

Indirect measures Sexual Functioning

of health: Mobility Self-care Dexterity Usual activities Cognition Interpersonal Digestion relations Skin & Disfigurement Social Bodily Excretion functioning Speaking Participation Breathing Fertility Energy & Vitality Sleep Communication

In order to operationalise the measurement of health, we need to define the set of domains that characterize health. Although domains of health may overlap, the aim is to identify a set of domains that is exhaustive as well as generally acceptable as the content of the ordinary meaning of health. Domains should not be wholly redundant, as would occur if all of the items in one domain could be fully explained by the items in other domains.

We may assume initially that all physiological functions fall within the realm of health. To assume this is not incompatible with a subsequent ranking of the health significance of some domains (since, for example, pigmentation of the hair may be of so little health interest that it need not be included in a domain of health). Not all changes in physiological function are instances of ill health. Some changes are so slight as to be insignificant (see Section V below),

7 and some of these changes, such as those associated with ageing (greying of hair or wrinkles) are, by virtue of the lack of further health ramifications, unremarkable.

The core domains of health must be distinguished from the consequences or impacts of a state of health on the well-being or other aspects of the life of an individual, especially if these are mediated through the physical or social environment. For example, an individual, because of a mental illness, may be socially isolated, with few friends or other interpersonal relationships. Although the various mental functions required to acquire and maintain relationships are components of health, the lack of relationships itself is a consequence of a health problem, not a health problem per se. Although this is clear enough, it is important to note that in some instances the best or only measurable phenomena that indicate the presence of a health problem may in fact be consequences that are outside the realm of health, a consideration that needs to be kept in mind when operationalizing domains of health.

Domains of health for the purpose of measuring health and to arrive at a parsimonious set need to be selected using the following guiding principles. They should be:

• valid in terms of intuitive, clinical and epidemiological concepts of health • linked to the conceptual framework of the ICF • amenable to self report, observation or measurements • comprehensive enough to capture all important aspects of health states that people value • cross-population comparable

Existing health state measurement instruments have differed considerably in their content in an attempt to arrive at a set of domains that covers the universe of health adequately. They have often combined domains of physiological function with other domains of well being. In developing the health status module for the WHO Household Survey program (16), WHO has attempted to develop a parsimonious set of domains based on the above principles. The current full health status module includes all the health and health-related domains listed in Figure 4.

Amongst the domains listed in Figure 4, it may be argued that some directly assess health (eg. hearing, vision, breathing, pain, etc.) while others such as work and household activities may be considered as proxy measures of health states. Across both types of domains, affect, cognition, mobility, pain, self-care, usual activities (including household and work related activities) have been included in almost all generic measures of health states: thus far, these domains form the core domains of the brief health status module included within the WHO Household Survey program. Based on these six domains, Figure 5 illustrates the multidimensional profiles describing health status through the first round of the WHO Household Survey program, for selected countries and surveys (18).

Eastern Mediterranean (9 countries) Former Socialist (13 countries) Latin American (9 countries) OECD subset (22 countries) 90

50 40 30

Estimated Level of Health of Level Estimated 20

0 Aff M Aff F Cog M Cog F Mob M Mob F Pain M Pain F Self M Self F Usual M Usual F Dom ains

Figure 5. Multi-dimensional Health Profile, WHO Health and Responsiveness Surveys 2000-2001, Selected surveys and countries

Descriptions of health states using domains provide a profile of health. A health state description thus differs from etiology-, symptom-, morbidity-, disease- or cause specific mortality-based classifications, such as those found within the International Statistical Classification of Diseases and Related Health Problems (ICD-10) (13). For example, an individual with the disease label “acute paralytic poliomyelitis, wild virus, indigenous” would be classified within one entry of the ICD-10 – viral infections of the central nervous system, acute poliomyelitis. Once the disease is no longer present, any lasting effects of the disease that the individual experienced or sequelae of poliomyelitis, would be classified within another entry – under sequelae of infections and parasitic diseases. Whereas the same individual regardless of disease status would have the level of his or her health assessed in each domain included within a multi-dimensional profile of health – such as within those domains listed as core domains in Figures 4 or 5.

The challenge for standardizing health state descriptions is to include all domains considered to be important in terms of societal health goals and in terms of health state valuation. When asked to value time spent in a health state for which key domains of health are not specified, a respondent must guess the average level in these domains and this will introduce measurement error and potential bias. At the same time, the amount of information that must be collected from populations and included in health state valuations must be minimised. This is done by attempting to identify a parsimonious set of domains of health that minimise overlap or redundancy

V. WHAT ARE WE MEASURING IN DOMAINS OF HEALTH?

Once a consensus is reached on what are the core domains to describe health, a valid, reliable and cross-population comparable approach to measure each domain must be developed. In order to do this, we require that each domain specify a sufficiently coherent construct that we can postulate an ordinal or cardinal scale for measuring that construct. Such a scale may be

9 measurable (where we can find appropriate measurement procedures), or latent (where we have categorical reports whether observed or self-report). So, for instance, we postulate that there is a latent mobility scale, depicted in the first column of Figure 6. For a given level of mobility, individuals in different populations (A, B or C) may well use different response categories on a self-reported survey question concerning mobility (17). If it is not possible to construct a single scale (latent or measured) for a domain, that is an indication that the domain is a compound domain including more than one important health construct. For example, inclusion of colour blindness in the domain of vision will probably lead to measurement problems, since colour blindness cannot be measured or reported on the same scale as visual acuity. If colour blindness turned out to be an important aspect of health for description or measurement, then it would be necessary to include it in the health state description as a separate domain.

A B C N

N Mi N Mo Mi

S Mi Mo

Mo E S

E E

Latent mobility N = None, Mi = Mild, Mo = Moderate, S = Severe, E = Extreme scale

Figure 6. Latent variable for a health domain: an illustration for mobility

Before further considering measurement issues, we first need to decide what contruct we are measuring in a given domain: performance or capacity. What is more useful and appropriate to compare: • Is it a particular state of experience, ie. performance in that domain in the actual environment? • Or is it the capacity for health, ie. ability in that domain in the relevant standard uniform environment (either in a test situation, or through self-report assessment or observation). Each of these perspectives may be useful under different circumstances, for example, in evaluating the impacts of certain types of interventions.

To the extent that performance reflects environmental barriers, , which may also vary with time and as individual circumstances change, it is probably not congruent with most notions of health. Thus, if a person cannot climb flights of stairs in their usual environment because they are too steep, most people would not say their health state had changed if the stairs were modified to be less steep. This is consistent with the notion of health as an attribute of individuals rather than environments (though these may be causal for health states). We

10 would not want to characterize the same cognitive impairment differently in two individuals simply because they have different vocations that call upon different types of cognitive tasks. Similarly, we would not say that an individual with a hearing impairment is healthier simply because she avoids noisy gatherings. These examples point to a common-sense understanding of health that does not correspond to performance because it excludes the idiosyncracies of an individual’s environment.

On the other hand, many societies commonly understand personal aids such as pacemakers, glasses, hearing aids to improve health states for relevant domains. The distinction here is between interventions that stay with the person, and those that stay with the environment. Thus, for a person with near vision problems affecting reading, a laser operation to modify the cornea would improve health state, provision of contact lenses or glasses would improve health state, but increasing the font size of all print in the person’s local environment would not be seen as an improvement in health state.

The notion of capacity corresponds more closely to this common-sense interpretation of health by defining external environmental factors in a uniform way. More specifically, we believe that capacity with an individual’s currently available personal aids is the most appropriate construct, as many societies commonly understand personal aids to improve health levels on relevant domains. This form of capacity with personal aids corresponds to the third qualifier in the ICF, whereas capacity without personal aids is the second qualifier.

Capacity without aids is not an appropriate choice for the construct of health. Let us consider the domain of visual acuity. If the counterfactual environment excludes currently available glasses, then the provision of glasses cannot be defined to improve health (=capacity). We thus propose that within a domain, the construct that we should measure is capacity with aids: the counterfactual environment is one in which external environmental factors are defined in a uniform way but in which the person is assumed to have their currently available personal aids and appliances. Thus individual aids and appliances are conceptualized as improving health by improving the person’s ability to perform the relevant domain function, and hence to improve the health state of the individual.

There is some arbitrariness here in defining the boundary between personal aids and environmental modifications. The GBD project drew the line at simple aids that should in principle be available to all people (including simple crutches, non-powered wheelchairs, glasses and standard hearing aids). Arbitrariness is acceptable in defining health states, if the boundary is set appropriately in relation to societal perceptions of what constitutes health, but the problem comes from different people envisioning different aids in the absence of explicit description of what is/is not included. As long as that is done, there is not a problem. Then somebody with a wheelchair actually has better mobility (capacity and performance) than somebody without, so is in a different health state.

Should the normative environment for assessment of domain capacity be a global standard or vary across different regions or countries? For example, should the normative uniform environment for assessment of mobility include a global standard provision of ramps for wheelchairs, or should the standard for developed countries reflect the greater provision of ramps (so that the health improvement resulting from providing a wheelchair to a person with paraplegia would be greater in developed countries than in developing countries)? We would argue that a single global standard should be used for all health domains. Thus, in the vision

11 domain, provision of glasses would result in the same health improvement, and would not depend on the average level of illumination at night in different countries.

Ideally, it would be made explicit in the measurement process whether the quantity under measurement is capacity or performance. In practice, there will be a high degree of correlation between these three and it may not be necessary to make these subtle distinctions in self- report questions. For domains comprised of more complex tasks, such as usual activities and self care, in actual practice it may be easier to measure performance rather than capacity with or without usual aids, and hence, they have been labelled as health-related domains in Figure 5.

In order to ensure that the measurement of health states is comparable across cultures and across nations it is necessary to ensure that the measurement of capacity in health domains results in cross-population comparable data. Since much of this data is gathered from self reports another major measurement issue is the adjustments for cut-point shifts that occur across populations when people select categorical response categories to report on the level of the underlying latent domain variable. It is clear that results from surveys that collect such information are not comparable without adjusting for such biases (17, 18).

No “gold standard” measurement technique exists to assess performance or capacity in most core health domains. Different domains may be measured by a combination of modes, or only through one mode using a range of tests, observations or questions, or only by a single test, observation or question (17, 18). Some core domains may be better measured by proxy measures – such as on health related domains.

VI. THE BOUNDARIES OF GOOD HEALTH

Another issue that needs to be addressed in operationalizing a definition of health is whether all increments and decrements on a domain are understood as improvements and losses of health, respectively, or whether there is some threshold above which increments and decrements are not perceived as changes in a person’s health state. For example, should one consider a person with an IQ of 180 as being healthier in the domain of intellectual functioning than another individual with an IQ of 150? Or should one say that the former is not necessarily healthier by virtue of a capacity that exceeds some norm for cognitive excellence? We believe that the concept of a threshold for full health accords better with commonly held societal views of health than an allowance for unbounded improvements in domain capacities to be considered as improvements in health. The ‘supra-health’ levels are perhaps better referred to as talent.

This is of relevance to the construction of measures of population health that accord with common notions of health and also common perceptions of the instrinsic value of health (for example, health may be perceived as a basic right or a human right, and societies as having some moral obligation to direct resources towards improvement of health). We argue that the concept of a threshold of full health accords better with comonly held societal views of health and priorities for health system interventions than a conceptualisation of unbounded improvements in capacities being labelled as health improvements.

As used in the ICF, disability no longer refers to limitations of performance or capacity in a set of domains defined in terms solely of tasks or activities, but is an umbrella term also

12 embracing impairments in domains of body functions and structures, and referring to decrements below some domain-specific norm. While we could specify separate cut-points on the domain scale for loss of health and for disability, there seems no compelling reason not to use the same cut-point and identify disability in a domain with less than full health in that domain (Figure 7). Because the ICF includes a larger set of health-related domains that go beyond direct domains of health, disability can refer to limitations of performance in non- health domains. Thus a person could have disability (on non-health domains) but full health (in the subset of health domains). On the contrary, if a person has less than full health, then the person also has disability.

Domain scale (measured or latent)

Full health

Less than full health

(Disability)

Figure 7. Health and disability in a single health domain

Some have argued that the cutpoint for full health can be identified purely in biological terms by examining the statistical distribution of functioning in the domain (19). Others have argued that the judgement of whether one individual is healthier than another can only be understood in terms of the ability to realise one’s vital goals (20). It seems clear to us that the domain threshold for full health is a normative choice: there is no criterion that would allow us, a priori, to choose a particular point on the population distribution of domain capacity as representing the threshold for full health. Further, this normative choice should reflect common perceptions that health is both intrinsically valuable and instrumentally valuable to human beings. We therefore suggest that the identification of thresholds for domain capacity should be empirically-based and linked to health state valuations (see Section VI). In intuitive terms, the threshold for a particular domain is the level of capacity below which a majority of people generally recognize decrements as departures from excellent health. In practice, average health state valuations for levels of capacity close to or above the threshold level will be extremely close to the value for full health, so that it is not necessary to explicitly delineate each domain threshold.

13 IV.2 Health states and disease and injury causes

Epidemiological information gathering has focused on the prevalence and incidence of disease conditions or morbidity and the causes and risk factors associated with these health conditions. Additionally information has been regularly gathered about the causes of death amongst populations. This epidemiological information taken together is intended to provide estimates of the extent of health (or ill health) in a population. Starting from epidemiological analyses of the incidence, prevalence and duration of specific disease and injury conditions in order to estimate the incidence or prevalence of health states involves the mapping of disease or injury stages, severity levels and sequelae into health states. In many cases, this mapping is implicit and incidence or prevalence statistics are all that is reported.

However, certain limitations of these epidemiological approaches need to be recognized in the context of the overall strategies to measure health. Firstly, health outcomes need to be understood separately from diagnosis or disease states in that the same diagnosis may be associated with very different levels of health in different individuals or in the same individual at different points in the course of the disease. For example, though it is estimated that about 2% of the world’s population has unipolar depression at any given point in time, all these persons have very different levels of physical, mental and social functioning. Similarly a person with diabetes in the initial course of the illness may be fully functional with just some dietary restrictions and exercise whereas progressively may go on to have renal failure and retinopathy that severely limit the person’s functioning. In other words, information beyond diagnosis is critical to understanding levels of health at the individual and population levels. This is important to recognize since the aggregated information in a population if one were to measure loss of health associated with all prior disease and injury ought to be consonant with the information that would be obtained if the health states of different individuals in the same population were to be measured.

Moreover, it is necessary to separate the notion of health from the determinants of health. Factors, both physical and behavioural, that cause decrease in health or ill-health cannot be construed as measures of the health of people. For example, tobacco use may lead to respiratory problems. In such situations the risk factor of tobacco needs to be understood as distinct from the disease it causes. In order to be able to influence health we need to separate the actual health status of people from the factors that influence the health state to allow the examination of this relationship in a systematic manner.

VII. VALUATION

In the conceptual framework elaborated in this paper, health states are described in terms of levels on multiple dimensions such as mobility, pain, hearing and seeing (see for example Figure 5). We may also derive, for any given health state described by such a multidimensional profile, a scalar index of the overall level of health associated with this state, measured on a cardinal scale that ranges from zero (for a state equivalent to death) to unity (for a state of ideal health). These health state valuations allow meaningful comparisons of differences between health states where health state profiles may not provide an unambiguous ordering. The mapping between multiple domains of health and health state valuations reflects the relative weights that individuals place on different domains of health, which may include complex interactions between levels on various domains (21).

Health state valuations, representing overall assessments of the levels of health associated with different states, provide the critical link that allows the non-fatal health experience of individuals to be combined with information on mortality in summary measures of population health (such as healthy life expectancy or disability-adjusted life years, among others). These weights formalize the intuitive notions that health levels lie on a continuum and that we may characterize an individual as being more or less healthy than another at a particular moment in time. Health state valuations quantify departures from perfect health, i.e., the reductions in health associated with particular health states. It is important to emphasize that these weights do not measure the quality of life of people with disabilities and do not measure the value of a person to society.

In fact, there have been a variety of different conceptual interpretations of health state valuations that have led to considerable confusion in defining the basis for measuring and understanding these valuations. It is useful for us to contrast our conceptual definition of health state valuations with these other concepts.

Utility. Some health economists have explicitly defined health state valuations as measurements of the utility associated with health states. Utility, however, is defined somewhat circularly as that thing that is maximized when individuals behave according to the axioms of expected utility theory, which offer a set of principles relating to choice under uncertainty. If utility is conceptualized in terms of some construct of the goodness associated with a health state, then the question of whether this goodness is separable from the overall goodness of the person’s current life situation arises. John Broome (22) persuasively argues that the goodness of health and other aspects of well being are not separable.

Quality of life or well-being. The term quality of life (QoL) is used differently in health literature that in sociological literature. In the latter, quality of life or well-being refers to how good, desirable and enjoyable life as a whole is felt by the person in question (23). In this sense, it is a subjective feeling, something ‘felt’ or experienced, and should thus probably be distinguished from ‘goodness’ or utility.

Health-related quality of life. In health, the term QoL is generally used quite differently to refer to a multi-dimensional construct. There are very many QoL instruments that have been developed in the health field and these generally contain items that relate to symptoms, impairments, functional status, and health domains, as well as to emotional states (affect, well-being). This use of QoL is clearly inconsistent with the general use of the term, and so health researchers have taken to refering to this construct as health-related QoL. However, these researchers cannot be measuring quality of life, or well-being, in the more general sense, since it is a function not only of the health-related QoL domains, but also of other determinants and conditions. Because well-being is not separable into a health and non- health component that are independent, the correct measurement strategy would be to measure total well-being (if that were possible) and then to empirically determine the causal relationships with levels on health domains as well as on other determinants of well-being.

Health level We avoid these difficulties if we consider health state preferences or valuations to provide a scalar cardinal index of the overall level of health associated with a multidimensional health

15 state, defined in terms of a set of numbers quantifying capacity on each domain scale (eg. level of mobility, level of self-care, level of affect, level of pain and level of cognition).

In this conceptualization, health state valuations measure overall level of health (for a state specified in terms of a set of domain-specific capacities), not quality of life or well-being (or some subset of it). We do not think there is a need to explicitly define this scalar as a choice- based construct. It is quite possible to conceptualize it in Sen’s terms as a non-choice-based human capacity (24). Because there are not compelling arguments to guide us on the relative importance of various health domains to overall level of health (is a certain level of pain more important than a certain level of mobility?), preferences are the most convenient way to elicit information on health state valuations. They also have the advantage of explicitly using representative population information. Figure 8 summarizes our overall conceptual framework for health.

Health states Quality of life

Health Health Health Disease domain 1 domain 2 domain n Well- or being injury

Other determinants of quality of Risk factors life or well- and being determinants

Health state valuation

Figure 8. Conceptual framework for health

VIII. SYNTHESIS AND FUTURE DIRECTIONS

The challenge for the future lies in collecting the most optimum information on all aspects of the framework and finding the most effective strategy for combining this information.

Burden of disease analysis uses a disease-specific approach to estimate the incidence and prevalence of disability (states of less than full health) associated with a comprehensive and exhaustive set of health conditions. Starting from epidemiological analyses of the incidence, prevalence and duration of specific disease and injury conditions in order to estimate the incidence or prevalence of health states involves the mapping of disease or injury stages, severity levels and sequelae into health states defined in terms of domains of functioning. An iterative process and extensive consultation with relevant experts is required to ensure consistency of epidemiological estimates for most conditions.

This disease-specific approach combines the estimation of the prevalence of different health state associated with them and ensures the inclusion of all causes of disability. However, there are currently two major limitations with this approach: problems with comorbidities, and the data demands for mapping disease sequelae to health states. Comorbidity refers to the not uncommon situation where a person has two or more health problems that result in disability (either dependently or independently of each other). Substantial effort is required to improve on the estimation of the prevalence of non-independent comorbidity for epidemiologically based approaches since the levels of health in such situations are not necessarily described by a simple additive or multiplicative function.

With regard to measures of decrements in health as described on a multiple set of domains, besides the challenge of cross-population comparability referred to above, it is necessary to arrive at a more parsimonious set that will capture the breadth of individual health. Initial results from WHO surveys suggest that besides the core seven domains of pain, affect, cognition, mobility, self-care, usual activities (including household and work related activities) and, interpersonal relationships and social functioning, additional domains such as vision, hearing, energy and vitality, breathing and sleep may be sufficient to capture major variations in the health of individuals.

These domains could then form the basis for the descriptions of health states that could be used in future valuation exercises in order to better measure the levels of health of individuals and the average levels of health for populations.

IX. CONCLUSIONS

Health must be understood as being inextricably tied to states of the human body and mind, and as such distinct from extrinsic environmental features. Whenever we use phrases such as ‘healthy environments’ or ‘unhealthy behaviours’ we are not ascribing health to environments or behaviours, but the health states or conditions that they produce in individuals.

Finally, health is an attribute of individual persons. Of course, we can aggregate health over populations, but doing so does not imply that health is an attribute of the population.

17 Taken together, this conceptual framework supports the consensus view that health is more than a matter of the absence of specific disease or injury. It is also the presence of certain threshold levels of ability to carry out physical and mental actions and tasks in the current environment..

In summary,

• Health is an attribute of individuals, which is best operationalized as a multidimensional set of domains; • To obtain meaningful information on health and health interventions, the boundaries of the notion of health must be determined by identifying a set of core domains of health. • The threshold for loss of health in any given domain reflects norms or standards. • Health state description and measurement must be distinguished from (1) subjective evaluations of health; (2) consequences of health states; and (3) environmental impacts on health and other proximate or distal determinants of health.

In keeping with the above conclusions, WHO thus recommends that for measurement purposes, health be understood as a multidimensional phenomenon that can be narrowed to a core set of health domains, each characterized by a single cardinal scale of capacity (measured or latent, and including currently available personal aids). The overall level of health associated with the set of abilities (or capacities) on the core health domains may be characterized by a cardinal scale of health state valuations. These valuations quantify level of health, not quality of life, well-being or utility.

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