01 What is
Epidemiology?
Key learning objectives
By the end of this chapter you will be able to:
> explain the concepts of epidemiology
> distinguish between descriptive and comparative epidemiological studies
> distinguish between experimental and observational epidemiological studies
> understand the aims of epidemiology
> understand the epidemiological process
> relate to the history of epidemiology
> describe some of the major achievements in public health.
Key terms
Classification of epidemiological studies Epidemiology
Endemic Public health
Epidemic Research
Epidemiological process Scientific method
Epidemiological transition
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, 2 Epidemiology
Introduction
This book will introduce you to the basic language and principles of epidemiology, which
is the study of factors and processes that affect health and disease in human populations.
Epidemiological research delivers the basis for evidence-based medical intervention, ‘best
clinical practice’ or public health policy—be it in the form of simply describing occurrences
of diseases or as sophisticated modelling of interdependent factors affecting a specific health
outcome.
In times when decision-making in the health sciences is required to be more and more
evidence based, epidemiological research becomes increasingly important. Whether you are
studying or practising as a public health professional, a doctor, or an allied health professional,
the knowledge that you acquire by working through this book will enable you to read and
critically assess the scientific health literature pertinent to your specific discipline. This basic
skill is necessary for evidence-based decisions in all health sciences. We also hope it will guide
and inspire you to carry out your own research as an Honours, Master of Public Health, or
Doctoral student to add new knowledge to your particular health discipline.
This book is principally aimed at undergraduate as well as postgraduate students in all
health and allied health disciplines, and draws examples from a wide range of applied health
research, including, but not restricted to, public health, medicine, nursing, occupational therapy,
physiotherapy, and sports and exercise sciences.
While the content of the whole manuscript is recommended for all students, undergraduate
students may wish to omit some sections during their initial study. The sections essential at the
undergraduate level are those listed under ‘introductory level’ in the table on page xxix. At the
end of each chapter, further reading sections, including interesting or interactive websites, are
provided for readers who require additional information.
Defining epidemiology
The word epidemiology comes from the Greek terms epi (meaning upon, among), dēmos
(meaning people, district), and logos (meaning word, study), and literally translated means
‘speaking upon people’ or ‘the study of people’. Thus, in epidemiology, the fundamental unit
of observation is people, in contrast to animals, inanimate substances or microorganisms,
which constitute the basis of investigation in other areas of health research. In epidemiological
studies, information is usually collected from a group of people, several groups of people, or
sometimes just one person.
Over time there have been several definitions of epidemiology. The definition from the
Oxford English Dictionary, citing a source from 1873, is ‘that branch of medical science which
treats epidemics’. We will be working with a more modern definition of epidemiology, which
is given in Box 1.1.
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, Chapter 1 What is Epidemiology? 3
Definition of epidemiology Box 1.1
Epidemiology is the study of the occurrence and distribution of health-related events, states
and processes in specified populations, including the study of the determinants influencing such
processes, and the application of this knowledge to control relevant health problems.
> ‘Study’ includes surveillance, observation, hypothesis testing, analytical research, and
experiments.
> ‘Distribution’ refers to analysis by person, place, and time.
> ‘Determinants’ are all the physical, biological, social, cultural, and behavioural factors that
influence health.
> ‘Health-related events, states, and processes’ include outbreaks, diseases, causes of diseases,
behaviour such as use of tobacco, reactions to preventive regimens, and provision and use of
health services.
> ‘Specified populations’ are those with common contexts and identifiable characteristics.
> ‘Application … to control …’ makes the aims of epidemiology explicit—to promote, protect,
and restore health, and advance scientific knowledge.
Source: Based on Porta 2014
Following the definition of epidemiology given in Box 1.1, epidemiology studies the
distribution of diseases and tries to answer questions such as: ‘Who has the disease?’; ‘How
many people have the disease?’; ‘When did the disease occur?’; and ‘Where did the disease
occur?’. For example, assume researchers want to investigate survivors of stroke in Australia
with the longer term plan being to introduce a new occupational therapy intervention for
stroke survivors. In order to position their project appropriately, the researchers determine that
Australian men are somewhat more likely to have a stroke than Australian women, and that
males are more likely to have a stroke at a younger age (60–74 years) than women. They further
find that based on self-reported data from a 2003 survey, an estimated 346 700 Australians
have had a stroke at some time in their lives. The researchers also find that during the last two
decades mortality rates for stroke have halved for both men and women, and that there were
no marked differences in mortality rates for people from rural areas or regions of lower socio-
economic status (AIHW 2006; Fitzgerald 2005). All the information reported above on stroke
is epidemiological information collected using epidemiological principles. The data presented
address some of the typical questions used to describe the distribution of stroke: they refer to
person (age, gender, etc.), place (Australia urban and rural), and time (now and 20 years ago).
Epidemiology is also interested in determinants of diseases, which implies, in its narrowest
meaning, the identification of causes of diseases. These determinants are often called ‘exposures’,
‘risk factors’, or ‘risk markers’ depending on the kind of relationship under investigation and
how well a potential cause–effect relationship is clarified. Determinants of disease include all the
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, 4 Epidemiology
physical, biological, and behavioural factors that influence health, such as nutrition, biological
agents, toxic agents, the social environment, and medical practice. Epidemiological studies that
deal with the identification of determinants of disease are referred to as analytical studies. For
example, the researchers of the above-mentioned stroke study would be well aware that smoking,
physical inactivity, hypertension, and high cholesterol levels are determinants of stroke.
The definition in Box 1.1 refers to ‘health-related states or events’. These health-related
states or events incorporate more than diseases (e.g. stroke). Hence, epidemiology deals with
outcomes that can be diseases, behaviours (e.g. smoking or stopping smoking, physical activity,
activities of daily living), or well-being (e.g. quality of life, survival).
The definition given above is the definition of the International Epidemiological
Association and is not without controversy. Eminent epidemiologist and biostatistician Olli
Miettinen points out that epidemiology is ‘community medicine’ and an epidemiologist is ‘a
physician who practices community medicine…’ (Miettinen 2011). However, Miettinen also
describes the recent shift from community medicine to a much broader understanding of
epidemiology focusing on applied epidemiologic and clinical research. Although he stresses the
differences between an epidemiologist according to his definition and a person who conducts
epidemiologic research (‘nor is a scholar in the field of music by definition a musician’), he
Epidemic is different
from endemic, which also concedes that, ‘Epidemiological research may actually defy definition that is generally
is used to classify agreeable—objective in this meaning’ (Miettinen 2011).
infectious diseases that
are ‘always in a place’,
For centuries, humans worldwide suffered from outbreaks of infectious diseases, such
but not in epidemic as smallpox, malaria, or bubonic plague. The word epidemic was originally used as a name
proportions. For example,
for these outbreaks of infectious diseases, and epidemiology was concerned with epidemics,
measles can be endemic
within a population, that is, the occurrence of diseases in greater frequencies than would ‘normally’ be expected
but if it is introduced (Figure 1.1). The initial focus on infectious diseases is not surprising as infectious diseases
to a population with no
previous exposure or were, and in many countries still are, the most serious diseases in humans. Infectious disease
resistance, such as an epidemiology raises very specific questions about agents, transmission, and immunisation
isolated group of South
American Indians, it may
(see Chapter 2). Infectious disease epidemiology provided the first models for epidemiology,
cause an epidemic. with many of its general principles being adapted later to other areas of modern epidemiology.
F i g u r e 1 .1 A disease may be endemic within a population, with a relatively constant number
of cases, but an outbreak of the disease, causing a spike in the number of cases,
is an epidemic
120
100
Epidemic
Number of cases
80
60
40
Endemic
20
0
0 5 10 15 20 25
Time
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Epidemiology?
Key learning objectives
By the end of this chapter you will be able to:
> explain the concepts of epidemiology
> distinguish between descriptive and comparative epidemiological studies
> distinguish between experimental and observational epidemiological studies
> understand the aims of epidemiology
> understand the epidemiological process
> relate to the history of epidemiology
> describe some of the major achievements in public health.
Key terms
Classification of epidemiological studies Epidemiology
Endemic Public health
Epidemic Research
Epidemiological process Scientific method
Epidemiological transition
Oxford University Press Sample Chapter
01_BUE_EPI_2e_97318_TXT_SI.indd 1 15/07/15 1:31 PM
, 2 Epidemiology
Introduction
This book will introduce you to the basic language and principles of epidemiology, which
is the study of factors and processes that affect health and disease in human populations.
Epidemiological research delivers the basis for evidence-based medical intervention, ‘best
clinical practice’ or public health policy—be it in the form of simply describing occurrences
of diseases or as sophisticated modelling of interdependent factors affecting a specific health
outcome.
In times when decision-making in the health sciences is required to be more and more
evidence based, epidemiological research becomes increasingly important. Whether you are
studying or practising as a public health professional, a doctor, or an allied health professional,
the knowledge that you acquire by working through this book will enable you to read and
critically assess the scientific health literature pertinent to your specific discipline. This basic
skill is necessary for evidence-based decisions in all health sciences. We also hope it will guide
and inspire you to carry out your own research as an Honours, Master of Public Health, or
Doctoral student to add new knowledge to your particular health discipline.
This book is principally aimed at undergraduate as well as postgraduate students in all
health and allied health disciplines, and draws examples from a wide range of applied health
research, including, but not restricted to, public health, medicine, nursing, occupational therapy,
physiotherapy, and sports and exercise sciences.
While the content of the whole manuscript is recommended for all students, undergraduate
students may wish to omit some sections during their initial study. The sections essential at the
undergraduate level are those listed under ‘introductory level’ in the table on page xxix. At the
end of each chapter, further reading sections, including interesting or interactive websites, are
provided for readers who require additional information.
Defining epidemiology
The word epidemiology comes from the Greek terms epi (meaning upon, among), dēmos
(meaning people, district), and logos (meaning word, study), and literally translated means
‘speaking upon people’ or ‘the study of people’. Thus, in epidemiology, the fundamental unit
of observation is people, in contrast to animals, inanimate substances or microorganisms,
which constitute the basis of investigation in other areas of health research. In epidemiological
studies, information is usually collected from a group of people, several groups of people, or
sometimes just one person.
Over time there have been several definitions of epidemiology. The definition from the
Oxford English Dictionary, citing a source from 1873, is ‘that branch of medical science which
treats epidemics’. We will be working with a more modern definition of epidemiology, which
is given in Box 1.1.
Oxford University Press Sample Chapter
01_BUE_EPI_2e_97318_TXT_SI.indd 2 15/07/15 1:31 PM
, Chapter 1 What is Epidemiology? 3
Definition of epidemiology Box 1.1
Epidemiology is the study of the occurrence and distribution of health-related events, states
and processes in specified populations, including the study of the determinants influencing such
processes, and the application of this knowledge to control relevant health problems.
> ‘Study’ includes surveillance, observation, hypothesis testing, analytical research, and
experiments.
> ‘Distribution’ refers to analysis by person, place, and time.
> ‘Determinants’ are all the physical, biological, social, cultural, and behavioural factors that
influence health.
> ‘Health-related events, states, and processes’ include outbreaks, diseases, causes of diseases,
behaviour such as use of tobacco, reactions to preventive regimens, and provision and use of
health services.
> ‘Specified populations’ are those with common contexts and identifiable characteristics.
> ‘Application … to control …’ makes the aims of epidemiology explicit—to promote, protect,
and restore health, and advance scientific knowledge.
Source: Based on Porta 2014
Following the definition of epidemiology given in Box 1.1, epidemiology studies the
distribution of diseases and tries to answer questions such as: ‘Who has the disease?’; ‘How
many people have the disease?’; ‘When did the disease occur?’; and ‘Where did the disease
occur?’. For example, assume researchers want to investigate survivors of stroke in Australia
with the longer term plan being to introduce a new occupational therapy intervention for
stroke survivors. In order to position their project appropriately, the researchers determine that
Australian men are somewhat more likely to have a stroke than Australian women, and that
males are more likely to have a stroke at a younger age (60–74 years) than women. They further
find that based on self-reported data from a 2003 survey, an estimated 346 700 Australians
have had a stroke at some time in their lives. The researchers also find that during the last two
decades mortality rates for stroke have halved for both men and women, and that there were
no marked differences in mortality rates for people from rural areas or regions of lower socio-
economic status (AIHW 2006; Fitzgerald 2005). All the information reported above on stroke
is epidemiological information collected using epidemiological principles. The data presented
address some of the typical questions used to describe the distribution of stroke: they refer to
person (age, gender, etc.), place (Australia urban and rural), and time (now and 20 years ago).
Epidemiology is also interested in determinants of diseases, which implies, in its narrowest
meaning, the identification of causes of diseases. These determinants are often called ‘exposures’,
‘risk factors’, or ‘risk markers’ depending on the kind of relationship under investigation and
how well a potential cause–effect relationship is clarified. Determinants of disease include all the
Oxford University Press Sample Chapter
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1:31 PMCOUNT:
, 4 Epidemiology
physical, biological, and behavioural factors that influence health, such as nutrition, biological
agents, toxic agents, the social environment, and medical practice. Epidemiological studies that
deal with the identification of determinants of disease are referred to as analytical studies. For
example, the researchers of the above-mentioned stroke study would be well aware that smoking,
physical inactivity, hypertension, and high cholesterol levels are determinants of stroke.
The definition in Box 1.1 refers to ‘health-related states or events’. These health-related
states or events incorporate more than diseases (e.g. stroke). Hence, epidemiology deals with
outcomes that can be diseases, behaviours (e.g. smoking or stopping smoking, physical activity,
activities of daily living), or well-being (e.g. quality of life, survival).
The definition given above is the definition of the International Epidemiological
Association and is not without controversy. Eminent epidemiologist and biostatistician Olli
Miettinen points out that epidemiology is ‘community medicine’ and an epidemiologist is ‘a
physician who practices community medicine…’ (Miettinen 2011). However, Miettinen also
describes the recent shift from community medicine to a much broader understanding of
epidemiology focusing on applied epidemiologic and clinical research. Although he stresses the
differences between an epidemiologist according to his definition and a person who conducts
epidemiologic research (‘nor is a scholar in the field of music by definition a musician’), he
Epidemic is different
from endemic, which also concedes that, ‘Epidemiological research may actually defy definition that is generally
is used to classify agreeable—objective in this meaning’ (Miettinen 2011).
infectious diseases that
are ‘always in a place’,
For centuries, humans worldwide suffered from outbreaks of infectious diseases, such
but not in epidemic as smallpox, malaria, or bubonic plague. The word epidemic was originally used as a name
proportions. For example,
for these outbreaks of infectious diseases, and epidemiology was concerned with epidemics,
measles can be endemic
within a population, that is, the occurrence of diseases in greater frequencies than would ‘normally’ be expected
but if it is introduced (Figure 1.1). The initial focus on infectious diseases is not surprising as infectious diseases
to a population with no
previous exposure or were, and in many countries still are, the most serious diseases in humans. Infectious disease
resistance, such as an epidemiology raises very specific questions about agents, transmission, and immunisation
isolated group of South
American Indians, it may
(see Chapter 2). Infectious disease epidemiology provided the first models for epidemiology,
cause an epidemic. with many of its general principles being adapted later to other areas of modern epidemiology.
F i g u r e 1 .1 A disease may be endemic within a population, with a relatively constant number
of cases, but an outbreak of the disease, causing a spike in the number of cases,
is an epidemic
120
100
Epidemic
Number of cases
80
60
40
Endemic
20
0
0 5 10 15 20 25
Time
Oxford University Press Sample Chapter
COUNT:
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