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

a 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):

To 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.

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.

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.