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A short introduction to epidemiology Chapter 1: Introduction

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Title: A short introduction to epidemiology Chapter 1: Introduction


1
A short introduction to epidemiologyChapter 1
Introduction
  • Neil Pearce
  • Centre for Public Health Research
  • Massey University
  • Wellington, New Zealand

2
Chapter 1Introduction
  • Germs and miasmas
  • Risk factor epidemiology
  • Epidemiology in the 21st century

3
Public Health and Clinical Medicine
Individuals
Groups
  • Treatment
  • Prevention

Health services research
Medicine
Health education
Public health
4
Traditional Epidemiology
  • 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
  • (Last, 1988)

5
Chapter 1Introduction
  • Germs and miasmas
  • Risk factor epidemiology
  • Epidemiology in the 21st century

6
Snow on Cholera
  • Water Deaths From Death
  • Supplier Population Cholera Rate
  • Southwark 167,654 844 5.0 Vauxhall
  • Lambeth 19,133 18 0.9
  • Both 300,149 652 2.2

7
Snows Cholera Map
8
The Decline in TuberculosisDeath rate
9
Social and Economic Factorsand Health
  • Just as social changes were the major cause of
    decline in infectious diseases last century,
    social changes are also likely to be the most
    effective means of reducing chronic diseases such
    as heart disease and cancer.

10
Chapter 1Introduction
  • Germs and miasmas
  • Risk factor epidemiology
  • Epidemiology in the 21st century

11
Epidemiology Is a Population Science
  • Traditional epidemiology starts at the
    population level and the first step is to
    ascertain variations in the occurrence of disease
    within and between populations
  • Populations include not only countries, but
    geographical regions, demographic groups,
    communities, extended families, etc

12
Epidemiology Is a Population Science
  • Many of the major discoveries in
    cancerepidemiology followed the publication of
    Cancer Incidence in Five Continents in the
    1950s and1960s which generated new hypotheses
    about possible (population and individual) causes
    of cancer
  • Of the 30-40 known occupational carcinogens, all
    were discovered in epidemiological studies and it
    often took many years of laboratory work to
    subsequently establish the etiologic mechanism

13
Examples of the Top Down Approach
  • Cancer Incidence in Five Continents
  • Global comparisons of CDH
  • Global comparisons of asthma prevalence
  • The European Community Respiratory Health Study
    (ECRHS)
  • The International Study of Asthma and Allergies
    in Childhood

14
Levels of AnalysisTop-down Versus Bottom-up
  • Populations
  • Groups
  • Individuals
  • Organs
  • Cells
  • Molecules
  • Social science/
  • epidemiology
  • Clinical
  • Pathology/
  • biology
  • Molecular biology

15
The Top-down Approach
  • Starts at the population level in order to
    ascertain the main factors that influence health
    status within the population
  • Uses a structural model of causation,rather than
    a behavioural model or a biomedical model
  • Causation is seen as resulting fromprocesses and
    mechanisms that areinternal between
    externally-related independent objects

16
Modern Epidemiology
  • The study of the occurrence of illness
  • A systematic body of epidemiologic principles
    by which to design and judge epidemiologic
    studies has begun to form only in the last two
    decades
  • (Rothman, 1986)

17
Modern Epidemiology
  • Epidemiology is a generic method
  • The word populations is not necessary for its
    definition
  • The focus is on measuring individual
    exposure-disease associations
  • Certain study designs are most valid
  • We should focus on hypotheses that fit these
    study designs

18
Modern Epidemiology
  • Concentrates on studying individual
    riskfactors for disease
  • Clinical trial paradigm comparing exposed
    with non-exposed individuals
  • Emphasis on analytical rather
    thandescriptive studies
  • Emphasis on individuals rather than populations
  • Increasing emphasis on molecular biology

19
The Bottom Up Approach
  • Reductionist
  • Positivist
  • Focuses on understanding the individual
    components of a process at the lowest possible
    level and using this information as the building
    blocks to gain knowledge about higher levels
  • A vast stockpile of almost surgically clean data
    untouched by human thought

20
The Decline of Population Epidemiology
  • There is currently little interest in the
    population approach because
  • It is regarded as too political, old
    fashioned and uninteresting
  • There is a lack of support and funding
  • The success of risk factor epidemiology

21
Problems of the Risk Factor Approach Tobacco
22
Problems of the Risk Factor Approach Tobacco
  • The limited success of legislative measures in
    industrialised countries has led the tobacco
    industry to shift its promotional activities to
    developing countries so that more people are
    exposed to tobacco smoke than ever before.
  • Thus, on a global basis the achievement of the
    public health movement has often been to move
    public health problems from rich countries to
    poor countries, and from rich populations within
    the industrialised countries.

23
Problems of the Risk Factor Approach Tobacco
  • When a public health problem is studied in
    individual terms (eg. tobacco smoking) rather
    than in population terms (eg. tobacco production,
    advertising and distribution, and the social and
    economic influences on consumption) then it is
    very likely that the solution will also be
    defined in individual terms and the resulting
    public health action will merely move the problem
    rather than solve it.

24
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25
Problems of the Risk Factor Approach Asbestos
26
Problems of Modern Epidemiology Biomarkers
  • We are in the era of molecular research ...
    The use of molecular markers represents a quantum
    leap in the evolution of epidemiologic ideas
  • (Schulte, 1993)

27
Problems of Modern Epidemiology Scientific
Limitations of Biomarkers
  • Historical exposures
  • Individual temporal variation
  • Study size
  • What does a biomarker measure?
  • Increased likelihood of confounding

28
Problems of Modern Epidemiology
  • Epidemiology has largely ceased to function as
    part of a multidisciplinary approach to
    understanding the causation of disease in
    populations and has become a set of generic
    methods for measuring associations of exposure
    (risk factors) and disease in individuals.
  • If epidemiology is just about measurement then
    it can never claim to be a science.

29
Problems of Modern Epidemiology
  • Recent changes in the epidemiologic paradigm
    have changed, and have reflected changes in, the
    way in which epidemiologists think about health
    and disease.
  • The key issue has been the shift in the level of
    analysis from the population to the individual.

30
Chapter 1Introduction
  • Germs and miasmas
  • Risk factor epidemiology
  • Epidemiology in the 21st century

31
Epidemiology in the 21st century
  • The importance of context
  • Problem-based epidemiology
  • Appropriate technology
  • Epidemiology as a population science

32
Context Is Important
  • The populations which epidemiologists study
    are not just collections of individuals which are
    conveniently grouped for the purposes of study,
    but are instead historical entities.
  • Every population has its own history, culture,
    organisation, and economic and social divisions
    which influences how and why people are exposed
    to particular factors, and how they respond.

33
Context Is Important
  • Even when focusing on individual-level
    hypotheses, epidemiology is inevitably entangled
    with society and it is unscientific to study
    disease in the abstract.
  • To understand the causation of disease in a
    population it is essential to understand the
    historical and social context.
  • The assumption that universal dose-response
    relationships are the norm arises from the narrow
    interests and experience of Western
    epidemiologists.

34
The Importance of Context
  • There were large numbers of deaths amongst the
    indigenous people when New Zealand (Aotearoa) and
    other areas of the Pacific were colonised in the
    19th century
  • It is commonly assumed that these deaths were due
    to infectious diseases, and affected all
    populations
  • In fact, many populations experienced very few
    deaths
  • The main determinant of death from infectious
    disease was whether land was taken (and therefore
    the social systems disrupted)

35
Problem-based Epidemiology
  • The approach of problem-based medicine can be
    used in the teaching and practice of epidemiology
  • The appropriate methods should be chosen to fit
    the problem rather than letting the methods
    define the problem

36
Appropriate Technology theories
  • New theories or hypotheses may require new
    methods of measurement
  • As attention moves upstream existing
    epidemiologic methods will become inappropriate

37
Appropriate technology methods
  • It cannot be simply assumed that high-tech
    methods such as molecular epidemiology will be
    more valid than traditional questionnaires
  • There is a need for an evidence-based approach
    to the teaching and conduct of epidemiology

38
Appropriate Technology methods
  • Just as case-control studies were developed for
    risk factor epidemiology, new methods need to
    be developed for ecoepidemiology
  • We should focus on the important public health
    issues and use appropriate technology to address
    them

39
Appropriate technology Strategies
  • It cannot be simply assumed that a bottom-up
    approach will be more effective, particularly
    since the top down approach has been effective
    in the past

40
Epidemiology in the 21st century
  • The current danger for epidemiology is not the
    use of new techniques or micro-level analyses,
    but that these techniques may define which
    hypotheses are acceptable for study

41
All of the Different Levels of Analysis Are
Important
  • Population level studies are complementary to
    studies at the individual and micro-levels
  • Individual and micro-level studies have had some
    real successes
  • It is legitimate that people should work at the
    level appropriate to their training and interest
  • A multi-level approach may be particularly
    effective

42
Epidemiology in the 21st century
  • Susser suggests that epidemiology has been
    through three major phases and is now entering a
    fourth
  • miasma theory epidemiology (traditional)
  • germ theory epidemiology (traditional)
  • black box epidemiology (modern, risk
    factor)
  • global epidemiology

43
Epidemiological Paradigms
  • Traditional
  • Branch of public health
  • Demography/social science paradigms
  • Population level
  • Top down (structural, dialectical)
  • Intervention upstream
  • Modern
  • Branch of science
  • Clinical trial paradigm
  • Individual/molecular level
  • Bottom up (reductionist positivist)
  • Intervention downstream

44
Epidemiology in the 21st century
  • We need to reintegrate epidemiology into public
    health and restore the population perspective
  • This requires not just multi-level analysis but
    rather multi-level thinking
  • This multi-level thinking can be encouraged and
    fostered by a problem-based and evidence-based
    approach

45
A short introduction to epidemiologyChapter 1
introduction
  • Neil Pearce
  • Centre for Public Health Research
  • Massey University
  • Wellington, New Zealand
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