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 multi- dimensional 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.