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 EH89AG
Raj.Bhopal@ed.ac.uk
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
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
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”.
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
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?
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 biosocial-environmental science focusing on disease in
populations.
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?
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/or
help plan and deliver health care
and/or
help prevent and control disease
Category of underlying
difference: example of sex

Biological

Co-existing diseases

Behavioural

Social

Occupational

Economic

Health care
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?
Types of disease and reasoning
on sickness/disease X

Genetic

Infections

Congenital

Toxins

Degenerative

Nutritional Deficiency

Cancers

Immune disorders

Injuries
Epidemiological theory

Can you discern any theories which have
guided this chapter so far?

What general principles follow from these
theories?
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.





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
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.