What is epidemiology? Objectives

1. What is epidemiology?Raj Bhopal, Bruce and John Usher Professor of Public Health, Public Health Sciences Section, Division of Community Health Sciences,University of Edinburgh, Edinburgh EH89AGRaj.Bhopal@ed.ac.uk

2. What is epidemiology?Objectives You should understand: • The focus of epidemiology is on the pattern of disease and ill-health in the population • Epidemiology combines elements of clinical, biological, social and ecological sciences. • Epidemiology is dependent on clinical practice and sciences to make a diagnosis, the starting point of our work. • The goal of epidemiology as a science is to understand the causes of disease variation and use this to improve the health of populations and individuals. • The goal of epidemiology as a practice is preventing and controlling disease, guiding health and health care policy and planning, and improving health care in individuals. • Epidemiological variables should meet the purposes of epidemiology. • Epidemiology is based on theories

3. Overview of Epidemiology • Epidemiology is the science and practice which describes and explains disease patterns in populations, and puts this knowledge to use to improve health • The central paradigm of epidemiology is that patterns of disease in populations may be analysed systematically to provide understanding of the causes and control of disease • Epidemiology seeks out the differences and similarities ('compare and contrast') in the disease patterns of populations to gain new knowledge • Valid measurement of the frequency of disease and factors which may influence disease, and are therefore potential explanations for the observed patterns, is crucial to the epidemiological goal

5. Epidemiology: definition and strategy • The origin of the word epidemiology is unknown but it is derived from the Greek words meaning study upon populations (epi = upon, demos = people, ology = study) • Epidemiopathology (pathos is the Greek word for suffering and disease) would be more accurate but clumsy • Epidemic was used by Hippocrates • Last’s dictionary gives a detailed definition of epidemiology that includes these words “The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems”.

6. Uses of Epidemiology Currently epidemiology is seen as useful in: • yielding understanding of what causes or sustains disease in populations • preventing and controlling disease in populations • guiding health and health care policy and planning • assisting in the management and care of health and disease in individuals

7. Epidemiology as a science • What are the characteristics of a science? • Name and differentiate between some disciplines which are and are not sciences? • Is public health a science? • Is epidemiology a science? • Is there some aspect of a science which epidemiology does not fulfill?

8. The scope of Epidemiology as a science • Epidemiology is particularly relevant to medicine rather than laboratory science, but the increasing collaboration between geneticists and epidemiologists is changing the balance • Epidemiology is concerned with disease in populations. Humans live in societies, where behaviour and attitudes are shaped by interaction among people, which in turn are governed by the conventions and laws. Epidemiology is, therefore not only a bio-science but also a social science. • Populations exist in a physical environment which is a dominant force in determining health. The study of life in relation to the environment is ecology, so epidemiology is, in addition, the science of the ecology of disease. • The science of epidemiology, therefore, combines elements of biology, social sciences and ecology - a bio-social-environmental science focusing on disease in populations.

9. The epidemiological exposure variable • What qualities should an exposure variable have to make it worth pursuing in epidemiology? • How do the purposes and uses of epidemiology help to assess the potential value of a variable?

10. Criteria for a good epidemiological variable: age • Impact on health in individuals and population • Be measurable accurately • Differentiate populations in their experience of disease or health • Differentiate populations in some underlying characteristic relevant to health e.g. income, childhood circumstance, hormonal status, genetic inheritance, or behaviour relevant to health. • Generate testable aetiological hypotheses, and/or help in developing health policy, and/orhelp plan and deliver health care and/or help prevent and control disease

11. Category of underlying difference: example of sex • Biological • Co-existing diseases • Behavioural • Social • Occupational • Economic • Health care

12. Sickness X: examine the handout (see last slide) • What thoughts come into your mind about the nature of the sickness? • What kind of sickness/disease is it? • What kind of sickness/disease is it not? • What sort of factors could cause a sickness such as this? • Can you form a definition of this sickness X? • If not, how would physicians make a diagnosis? How could the number of cases of the sickness be counted? • If you can define it how would you do it? • What would be the components of your definition?

13. Genetic Congenital Degenerative Cancers Injuries Infections Toxins Nutritional Deficiency Immune disorders Types of disease and reasoning on sickness/disease X

15. Epidemiological theory • Can you discern any theories which have guided this chapter so far? • What general principles follow from these theories?

16. Epidemiological theories • disease in populations is more than the sum of the disease in individuals • populations differ in their disease experience • disease experiences within populations differ in subgroups of the population • disease variations can be described and their causes explored by assessing whether exposure variables are associated with disease patterns. • knowledge about health and disease in human populations can be applied to individuals and vice versa. • health policies and plans, and clinical care can be enriched by understanding of disease patterns in populations.

17. Summary • Populations, as with individuals, have unique patterns of disease. Populations’ disease patterns derive from differences in the type of individuals they comprise of, in the mode of interaction of individuals, and in the environment in which the population lives. • The science of epidemiology, which straddles biology, clinical medicine, social sciences and ecology, seeks to describe, understand and utilise these patterns to improve health. • Epidemiology is useful in other ways too, including preventing and controlling disease in populations and guiding health and health care policy and planning. • Epidemiology is both founded on, and contributes to, theories of health and disease, though these are seldom made explicit • Modern epidemiology is becoming more than a science; it is becoming a craft, vocation and profession; a partner of public health, not just a science of public health

18. Sickness X A sickness of unknown type, which appears as outbreaks, sometimes affecting whole communities, is spreading across a large part of continental Europe. Years later it will emerge in the USA. It will be shown to be present in many countries, though it may remain unrecognised in normal medical practice, for it may occur as solitary cases or in small numbers and not outbreaks. Sick people have a wide range of symptoms and signs on examination. Their many symptoms include simply feeling unwell, with loss of appetite and abdominal pain, disturbances of the gastrointestinal tract including diarrhoea, a skin rash on parts of the body exposed to the sun, and mental disturbances. It leads to progressive physical and mental deterioration. People who contract the sickness are likely to die, with the mortality rate as high as 60 percent in some outbreaks. If a sufferer recovers the sickness can recur.