Health and illness

Chapter 15
Health and illness


Definition of health

The World Health Organization (WHO 1948) has defined health as

imagea state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

This definition has not been amended since the WHO Constitution was adopted in 1946, and was re-affirmed by the Declaration of Alma Ata (1978). Few could disagree with it as an aspiration, but it does pose problems of whether everyone, at an individual and population level, can realistically achieve such a state. The WHO has gone on to discuss how health for all can be achieved, through the Ottawa Charter for Health Promotion (WHO 1986):

imageTo achieve a state of complete physical, mental and social well-being, an individual or group must be able to identify and to realise aspirations, to satisfy needs and to change or cope with the environment. Health is, therefore, seen as a resource for everyday life, not the objective for living.

The Charter also set out what it considered to be the prerequisites for health (Figure 15a).

The chapters in this section of the book cover the sources of data for describing and analysing health and its determinants and describe the health impacts of some of the main determinants. Many other factors also influence health; this book is not comprehensive in its coverage of information that may be relevant in assessing the health of a population. Health promotion is covered in Chapters 34 and 35.


Concepts and beliefs about illness vary widely within and between cultures and communities. Views of health professionals on the causation of illness, as well as on the best way to manage it, may also differ from those of the lay population and in some cases from those of other health professionals.

Whether or not a person seeks help from health professionals depends on many factors. Such factors include the nature and severity of the symptoms (people are more likely to seek help for symptoms that start abruptly or are perceived as worrying) and the disruption the symptoms cause to everyday activities such as work or childcare.

From a public health perspective, understanding health beliefs and why and when people consult health services is essential to plan and develop health services and preventive programmes that people will use and find effective. It is particularly important to understand why some population groups, referred to as ‘hard to reach’, do not use services and to consider ways in which they can be encouraged to do so. Some ethnic minorities, travelling communities and young single men can all be considered hard to reach for some services.

Disability, impairment and handicap

These three terms are useful in describing the actual physical problem caused by an illness (disability), the function that cannot be carried out as a result of that problem (impairment) and the resulting impact of that lack of function on the person’s life and everyday activities (handicap). Similar disabilities and impairments have very variable impacts on different individuals. For example, most people may be able to cope with the loss of a finger, but to a professional musician it may mean the loss of their livelihood.

Measuring health and illness

Many of what are termed measures of health are actually measures of illness. Routinely available health data include numbers and causes of death, diagnosed cases of specific diseases such as cancer or communicable diseases, prescribed drugs and contacts with health services, for example, consultations and hospital admissions.

General health is usually measured subjectively by asking people whether they are well or not. There are a number of standard questionnaire-based tools that can be used to measure general health in surveys, clinical trials or other research studies. Commonly used measures include the Short Form 36 (SF36), the General Health Questionnaire (GHQ), the EQ5D and the Nottingham Health Profile (NHP). The topic of measuring health and quality of life, particularly for use in economic evaluations, is covered in Chapter 38.

Illness can also be measured subjectively, by asking patients to rate their illness in terms of, for example, symptoms, symptom severity or ability to perform everyday activities. For instance, the UK census contains a question on whether people have any longstanding illness which limits their activities (Figure 15b). There are many tools available for use in specific diseases, for example, Beck’s Depression Scale and the St George’s Respiratory Questionnaire.

Estimates of disease prevalence or incidence will inevitably depend on which methods of disease measurement have been used. For every person who dies of a disease, more are admitted to hospital with severe symptoms, far more are treated in primary care without the need for hospital admission, and many more again are symptomatic but do not seek help from health services. It is also possible that people may have a disease without becoming symptomatic: serological testing of a population for chickenpox or influenza, for example, will reveal those who have been infected but who have no history of a relevant symptomatic illness. This symptom pyramid or iceberg is shown in Figure 15c.


Asthma is a common chronic disease characterised by variable wheeze and/or breathlessness, but it is not easily or succinctly defined, leading to difficulties in estimating prevalence. The following data demonstrate the difference in estimated prevalence, depending on the definition used:

Ever wheezed 33%
Wheezed in last 12 months 19%
Doctor-diagnosed asthma ever 21%

Source: The Burden of Lung Disease: A Statistics Report from the British Thoracic Society, 2006

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Oct 31, 2017 | Posted by in PUBLIC HEALTH AND EPIDEMIOLOGY | Comments Off on Health and illness
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