This document provides an overview of epidemiology, including definitions, key concepts, study designs, and examples from the history of epidemiology. It defines epidemiology as the study of health-related states and events in populations and applying this to disease control. Some key points covered include: - Descriptions of landmark epidemiological studies that advanced understanding of diseases like cholera, scurvy, lung cancer. - Explanations of common epidemiological study designs like cohort studies, case-control studies, and their strengths/weaknesses. - Details on the global burden of musculoskeletal disorders like back pain based on studies like the Global Burden of Disease. - Discussions of epidemiology's role in population health management

1. EPIDEMIOLOGY
- A BRIEF INTRODUCTION
- PAUL BARRATT

2. OVERVIEW
• What is epidemiology and epidemiological thinking?
• A brief history of epidemiology
• The burden of musculoskeletal pain on population
• A brief overview of epidemiological study designs
• Incidence vs. prevalence

3. EPIDEMIOLOGY, A
DEFINITION
“Epidemiology is the study of the distribution and
determinants of health-related states or events
(including disease), and the application of this study to
the control of diseases and other health problems”
(WHO 2006)

4. EPIDEMIOLOGICAL
THINKING
• Epidemiology is concerned determining if there is an association
between a characteristic or exposure and a disease. Conclusions
in epidemiology are based on comparisons.
• As a comparative science, it is necessary to have measures that
can be meaningfully compared
• Clues to aetiology come from comparing disease rates in groups
with differing levels of exposure
• Therefore, epidemiology thrives on heterogeneity. If everyone
smoked 20 cigarettes per day the link with lung cancer would
have been undetectable.

5. KEY ASPECTS OF
EPIDEMIOLOGICAL RESEARCH
• formulation of a research question and hypothesis
• selection of a study population
• critical evaluation of study designs (strengths and
weaknesses)
• skills needed to gather information
• exposure and outcome assessment
• recognizing potential sources of bias

6. TOOLS OF EPIDEMIOLOGY
• scientific methods for study/research
• techniques for collecting and organizing information
• information about the biological basis of health and
illness
• information about human behaviour that affects
health
• people skills needed to gather information

7. PURPOSES OF
EPIDEMIOLOGY
Population-based health management:
• to better understand the burden and causes of health
problems in target human populations
• to inform changes that decrease risk and improve
health

8. A BRIEF HISTORY
• Hippocrates (460 – 377 BC) “father of medicine”
Image: Wellcome Collection. Attribution 4.0 International (CC BY 4.0)
• first epidemiologist;
• sought a logic to sickness; examined relationships
between occurrence of disease and environmental
influences.
• described disease from rational rather than supernatural
basis.
• observed that different diseases occur in different
locations e.g. malaria and yellow fever mostly in swampy
areas
• introduced the terms epidemic and endemic

9. JOHN GRAUNT (1620-1674 AD)
• described disease occurrence and death with the use of systematic
methods
• developed early human statistical and census methods
• developed life tables and calculated life expectancy

10. THOMAS SYDENHAM
(1624-1689)
• approached study of disease from observational basis
rather than accepted traditional theories.
• didn’t identify causes of disease but advanced useful
treatments including fresh air, good diet and exercise
• other physicians rejected these at the time
Image: Wellcome Collection. Attribution 4.0 international (CC BY 4.0)

11. JAMES LIND
(1716-1794)
• ‘Treatise on Scurvy’ -identified symptoms of scurvy and
the fact that disease common in sailors.
• looked at the air and damp living conditions as a possible
cause.
• compared their experience with healthy subjects
• set up controlled experiments with diet and observed
that citrus fruit most effective in reversing symptoms.
Image: Wellcome Collection. Attribution 4.0 International (CC BY 4.0)

12. JOHN SNOW
(1813-1858)
• ‘Father of modern epidemiology’; traced source of a cholera
outbreak in Soho, London 1854.
• sceptic of the widely held ‘miasma’ theory.
• identified source as public water pump on Broad Street drawing
water from sewage-polluted sections of the Thames
• major event in history of public health and geography and
• regarded as founding event in the science of epidemiology
Image: Wellcome Collection. Attribution 4.0 International (CC BY 4.0)

13. A variant of the original map made by John Snow in 1854.
Cholera cases are highlighted in black.
Image: Wellcome Collection. Attribution 4.0 international (CC BY 4.0)

14. BRITISH DOCTORS STUDY
1954
• led by Richard Doll and Austin Bradford Hill
• prospective cohort study
• lent very strong statistical support to the suspicion
that tobacco smoking was linked to lung cancer.

15. GLOBAL BURDEN OF
DISEASE STUDY
• GBD 2010, (Lancet Dec 2012)
• largest ever systematic effort to describe the global
distribution and causes of a wide array of major disease
• aims: “new, robust, and reliable estimates of burden for
all major diseases, injuries, and risks that are widely
disseminated, understood, and easily used by
policymakers, researchers, funders, and practitioners”
• underway since 2008 >175 diseases and injuries, 20 risk
factors
• >480 experts globally

16. MUSCULOSKELETAL PAIN
• The second greatest cause of disability after mental and
behavioural disorders (GBD 2010)
• includes joint diseases such as osteoarthritis and rheumatoid
arthritis; back and neck pain; osteoporosis and fragility fractures;
soft tissue ‘rheumatism’; injuries due to sports and in the
workplace; and trauma
• pain, physical disability and loss of personal and economic
independence

17. CURRENT ESTIMATES OF PEOPLE
AFFECTED WORLDWIDE
(LANCET 2012) IN MILLIONS
0
100
200
300
400
500
600
700
Back pain 632 Neck pain 332 Osteoarthritis
knee 251
Other 561

18. MAIN CONTRIBUTORS BY YEARS LIVED WITH
DISABILITY (YLD)
IN MILLIONS
0
20
40
60
80
100
Low back pain 83.1 Neck pain 33.6 Osteoarthritis 17.1

19. RANKING OF MAJOR CAUSES OF
DEATH AND DISABILITY
(% DALYS - DISABILITY ADJUSTED LIFE
YEARS)
0
5
10
15

20. OTHER GBD FINDINGS
• Disability due to musculoskeletal disorders is estimated
to have increased by 45% from 1990 – 2010
• Osteoarthritis is the fastest increasing major health
condition
• This relates to ageing of the population, increased
obesity and lack of physical activity
• incidence of low back pain (LBP) is highest in the third
decade, prevalence increases with age until the 60–65
year age group and then gradually declines (Hoy et al
2010 for GBD)

21. OTHER REPORTED RISK
FACTORS FOR LBP
• low educational status
• stress, anxiety, depression,
• job dissatisfaction, low levels of social support in the
workplace
• whole-body vibration.
(Hoy et al 2010)

22. OTHER GBD FINDINGS
• Working age people with long-term back problems
were more than two and a half times more likely not
to be in the labour force
• With three or more additional conditions, this goes up
substantially – more than nine times more likely not to
be in the labour force

23. COSTS
• Musculoskeletal pain costs £30 billion in the UK
• Of which £12.3 billion back pain
• £584 million on prescriptions for pain in UK (CMO
2008)
• MSK disorders cost 2% of the EU domestic product
• 49.9% of total cost of sickness absence in Europe
lasting longer than 3 days (Bevan et al 2009)

24. EPIDEMIOLOGY CONTRIBUTION
TO POPULATION-BASED HEALTH
MANAGEMENT
• Assess health states and health needs of a target
population
• Implement and evaluate interventions designed to
improve the health of that population
• Efficiently and effectively provide care for a population
consistent with community's culture, policy and health
resource values

25. CHALLENGES IN
EPIDEMIOLOGICAL
INVESTIGATIONS
• difficulties in defining and measuring the disease
• imprecision determining the time of onset
• prolonged intervals between exposure to agent and
onset (induction period) and between disease onset and
detection (latency)
• multi-factorial disease aetiology
• differential effect of factors and course of disease.

26. PRINCIPAL TYPES OF
EPIDEMIOLOGICAL STUDY DESIGN

27. COHORT STUDY -
PROSPECTIVE
• Longitudinal study - observing the temporal order of
events
• follows a group of healthy people with different levels
of exposure and assesses what happens to their health
over time
• Used to assess incidence
• Effect measure: risk ratio (or relative risk) = ratio of the
risk in the exposed ÷ risk in the unexposed

28. COHORT STUDY -
PROSPECTIVE
ADVANTAGES
• Ethical – people not deliberately
exposed to risk factors
• recall bias minimized
• exposure precedes the health
outcome — a condition necessary
for causation
• useful for relatively common
diseases
DISADVANTAGES
• potential large sample size
• outcomes must be determined as
they develop
• portion of the cohort may be lost
(selection bias)
• potential exposure/outcome
misclassification (measurement
bias)
• Expensive and time consuming

29. COHORT STUDY -
RETROSPECTIVE
• Exposure and subsequent outcome have already
occurred in the past
• collect the data now and establish risk of developing a
disease if exposed to a particular risk factor
• examines possible risk and protection variables in
relation to a result that is already established

30. COHORT STUDY -
RETROSPECTIVE
ADVANTAGES
• Can be smaller scale
• require less time to complete
• better for analysing multiple
outcomes
• Can address rarer diseases
with smaller sample size -
diseased people identified at
outset
• Not expensive
DISADVANTAGES
• temporal relationship difficult
to assess
• Selection bias of controls
possible
• misclassification bias possible
owing to retrospective aspect
• need to rely on others for
accurate record-keeping

31. CASE CONTROL STUDY
• compares subjects who have condition or disease
("cases") with those who do not but are otherwise
similar ("controls") with regard to how frequently a
factor or attribute is present
• used to identify risk factors (variables associated with
increased risk of disease)

32. CASE CONTROL STUDY
ADVANTAGES
• Useful for rare health
outcomes
• Quicker and cheaper than
cohort study
DISADVANTAGES
• Selection bias possible
• Controls may not be
comparable to cases
• Recall bias possible
• results may be confounded by
unobserved factors
• weak evidence for causal
inferences

33. CROSS SECTIONAL STUDY
• Descriptive
• observation of all of a population, or a representative
subset, at a defined time
• compares group members in terms of their current
health & exposure status
• preliminary data to support further research
• used to assess prevalence
• effect measure: odds ratio (OR)

34. CROSS SECTIONAL STUDY
ADVANTAGES
• provides data on the entire
population under study
• relatively quick and easy to
conduct
• Large studies at relatively low
cost
DISADVANTAGES
• descriptive so cause-and-
effect relationships cannot be
inferred
• data collection may be a
source of report or recall bias
• may be considerable cohort
differences

35. CASE SERIES (OR CLINICAL
SERIES)
• Descriptive study
• Tracks patients with known exposure given similar
treatment or-
• examines medical record for exposure and outcome
• Is retrospective or prospective
• Single patient or small number of patients
• Consecutive (all patients reporting to author) or non-
consecutive (a selection)

36. CASE SERIES
ADVANTAGES
• May identify unusual feature
leading to new hypothesis
• Useful when a disease is
uncommon
• May be first to provide clues
for new disease or adverse
effect
DISADVANTAGES
• Cannot make inferences
about general population
• May be confounded by
selection bias
• Calculations of absolute or
relative risk not possible

37. Incidence vs. Prevalence
PREVALENCE
• Proportion of population found to
have condition:
• at a specific point in time –(point
prevalence) or
• at some time during a specified
period – (period prevalence)
• Expressed as percentage or
proportion
• Cross sectional studies
INCIDENCE
• Measure of risk of developing a
condition within a specified time
• Incidence proportion = number
new cases within a time period ÷
size of the population initially at
risk
• Expressed as percentage or
proportion per time period
• Longitudinal studies

38. Incidence vs. Prevalence
cont.
•
Incidence conveys information about risk of contracting
the disease, whereas prevalence indicates how
widespread the disease is.
• When studying possible aetiology of a disease, better to
analyse incidence, since prevalence doesn’t provide a
pure measure of risk.
• However, longitudinal studies, which measure incidence,
are more lengthy & expensive than cross sectional
studies which measure prevalence.

39. HIERARCHY OF EVIDENCE
• The relative weight carried by the main types of epidemiological
study puts them in the following order (from strongest to
weakest):
1 cohort studies
2 case control studies
3 cross sectional studies
4 case reports
(Greenhalgh 2010)

40. REFERENCES
Bevan S, Quadrello T, McGee R, Mahdon M, Vavrovsky A and Barham L, (2009). Fit for
Work? Musculoskeletal Disorders in the European Workforce. London: The Work
Foundation.
Chief Medical Officer (CMO) Annual Report (2006)
Doll R, Hill AB. (1954) The mortality of doctors in relation to their smoking habits, BMJ 328
(7455): 1529
Global Burden of Disease study 2010 The Lancet, Vol 280 Issue 9859 Pages 2053 - 2054, 15
December 2012
Hoy D, Brooks DP, Blythe F, Buchbinder FR, The Epidemiology of low back pain Best Practice
& Research, Clinical Rheumatology 24 (2010) 769–781
WHO Library Cataloguing-in-Publication Data, Basic epidemiology. Bonita, R. Beaglehole,
Kjellström T, 2nd edition.1.Epidemiology III.World Health Organization. 2006