This document provides an overview of epidemiology and public health. It discusses the definition of epidemiology as the study of the distribution and determinants of health-related states or events in populations. Epidemiology is used to describe disease occurrence, identify risk factors, and evaluate interventions. Key concepts covered include levels of prevention, health determinants, indicators, risk factors, and measures of population health. The document also summarizes different epidemiological study designs including observational and experimental studies and their ability to prove causation. Potential sources of error in epidemiological studies are also discussed.

1. Prof S P Patel, C.M. & Public
Health, KG Medical University
UP, Lucknow-226008
EPIDEMIOLOGY
pervades
PROFESSIONAlISM
((The role of cognitive dissonance and volition _ medical & health science)The role of cognitive dissonance and volition _ medical & health science)

2. “A community is a democratic only when the
hum best and the weakest person can enjoy
the best civil, economic and social rights
that the biggest and the most powerful
process”
-A Philip Randolph-

3. Part 1:
Basic Health
Epidemiology

4. EPIDEMIOLOGY
Greek words: EPI , “upon”
DEMOS, “people”
LOGOS : “study”
(But here we will study to human infirmities)

5. Epidemiology and Public Health
Public Health, broadly speaking, refers to
collective action to improve population
health[1].
Health epidemiology , one of tools for
improving public health, is used in several
ways as: Causation of disease, Natural
history of disease, health status of
populations and Evaluating intervention.
Ref: Beaglehole R, Bonita R. Public Health of Crossroad: achievements and
prospects, Cambridge University Press.2004

6. Focus of Population:
Level of
Prevention:
1- Primordial
 Intervening to
Lifestyle
2-Primary
Health promotion
 Specific preven.
Nutrition interven
Safe water&sanitation
3-Secondary
ED & Treatment
4-Tertiary
Disability limitation
&Rehabilitation

7. Health Epidemiology and Human
Health:
Early Staze: Early studies in
epidemiology were concerned with
causes (etiology) of communicable
diseases and it can lead to the
identification of preventive methods. In
this sense, health epidemiology is a
basic medical science with the goal of
improving the health of populations.
Basic Terms:

8. Good Health Poor HealthPoor Health
Genetic factorsGenetic factors
Include:
1.Biological
2.Chemical
3. Physical
4.Economical
5.Cultural
Personal
behaviors
interplay
1: Causation of disease1: Causation of disease
Epidemiological ways
Environmental
factors

9. 2: Natural History of disease2: Natural History of disease
Good
Health
Subclinical
changes
ClinicalClinical
changeschanges
Death
RecoveryRecovery
3: Health status of3: Health status of
populationpopulation
Genetic
factors
Environmental
factors
Epidemiological ways
Proportion
with ill health
Time

10. 4: Evaluating interventions
Good Health Ill Health
Treatment,
Medical care
Health promotion
Preventive measures
Public health services

11. Definitions:
“The science of the mass phenomena of
infectious diseases”. (Frost, 1927)
“The study of the distribution &
determinants of disease frequency in
man”(Mac Mohan,1960)
“TheThe study of the distribution &study of the distribution &
determinantsdeterminants of health related states orof health related states or
events in specified populations and theevents in specified populations and the
application of this study to control of healthapplication of this study to control of health
problems”problems” (John M Last,1988).

12. Epidemiology is theEpidemiology is the study of factorsstudy of factors
affectingaffecting the health and illness ofthe health and illness of
populations, andpopulations, and serves as theserves as the
foundation of logic of interventionfoundation of logic of interventionss
made in the interest of public healthmade in the interest of public health
and preventive medicine.and preventive medicine.
(Wikipedia)

13. History of epidemiology
06/17/1513
In the 1900s health epidemiologists extend their methods to non
infectious diseases and studied effect of behaviors and life style in
human health. There are some important achievements in health
epidemiology, these are;
John Snow and cholera epidemic in London in 1848-1854.
Framingham heart study started in 1950 in Massachusetts, USA and still continuing to
identify the factors leading to the development of the coronary heart diseases.
Smoking and lung cancer by Doll and Hill in 1964.
Polio Salk vaccine field trial in 1954 to study the protective efficacy of vaccine in a million
school children.
Methyl Mercury poisoning 1950s In Minamata
Brief about epidemiological action by John Snow
Snow believed that cholera is transmitted through contaminated water. He began his
investigation by determining where in this area person with cholera lived and worked. He
then used this information to map for distribution of diseases. Then ,Snow believed that
water was the source of infection for cholera. He marked the location and searches the
relationship between cases and water sources. He found that cholera was transmitted
though contaminated water. This was the major achievement in epidemiology.


14. Can this cost effective early epidiologicalCan this cost effective early epidiological
observation beobservation be inspiringinspiring to usto us
 Special features of given effort
 During: 1848-49 and 1853-54
 Initiated by John Snow
 Taken problem was Cholera deathsCholera deaths
 Meticulous Research out come (factor effecting) was Contaminated waterContaminated water
supplysupply
 Interpretation was improvement of water supplies and sanitation.Deaths from Cholera in Districts of London supplied by two water companies, 8
july to 26 August 1854
Water supply
company
Population in 1851 No. of Cholera
Deaths
Cholera Death Rate
(per 1000 population)
Southwark 167654 844 5.0
Lambeth 19133 18 0.90.9

15. Basic TenetsBasic Tenets (Principles)(Principles) ofof
epidemiologyepidemiology
06/17/1515
A. Target of a study in epidemiology is human Population as
Geographical area, Age, Sex, Ethnicity, Race etc.: the
most common population in epidemiology is the
population is a given area or country at a given time.
Since the structure of population varies at each time such
variations also have to be taken in to consideration during
data analysis.
B. All findings must relate to the defined population.
Enumeration is not enough in epidemiology, the
population at risk of developing that diseases need to be
enumerated as well.

16. Continue.
06/17/1516
C. Conclusions are based of comparisons: comparing
the rates of diseases frequency among the exposed
and unexposed and the unexposed is an important
epidemiological method.
D. Description of events by time, place and person.
Getting answer for when, where and who are
affected is very important in epidemiology to
formulate hypothesis about its causation. Other
important aspects are what, why and how of the
events.

17. Aims of Epidemiology (Health)
06/17/1517
According to the International Epidemiological Association
(IEA) Epidemiology has three main aims.
To describe and analyze diseases occurrence and
distribution in human populations;
To identify etiological factors (Risk Factors) in the
pathogenesis of diseases;
To provide the data essential to the planning,
implementation and evaluation of services for the
prevention, control and treatment of diseases and to
the setting up of priorities among those services.
o

18. THETHE ULTIMATEULTIMATE AIM:AIM:
To eliminate or reduce the healthTo eliminate or reduce the health
problem or it’s consequences.problem or it’s consequences.
To promote the health of deferentTo promote the health of deferent
community peoples by providingcommunity peoples by providing
high quality of health serviceshigh quality of health services
through answerable authoritiesthrough answerable authorities

19. Uses of epidemiologyepidemiology
06/17/1519
 Description of the health status of the populations. It includes
proportion with ill Health, change over time, change with age
etc.
 Evaluation of the interventions.
 Planning health services, Public policy and programs.
 Epidemiologists have become involved in evaluation the
effectiveness and efficacy of health services, by determining
the appropriate length of stay in hospital for specific
conditions, the efficiency of sanitation measures to control
diarrhoeal diseases, etc.

20. 06/17/1520
Field of epidemiology
Epidemiology covers the various types of field in
different types of activities. It is applied in every field
as Medical, Health, (Agricultural, Economics, ) etc. They
are as:-
Clinical epidemiology
Public health epidemiology
Social epidemiology
Environmental epidemiology
Descriptive epidemiology
Analytical epidemiology
Experimental epidemiology
Communicable diseases epidemiology
Non-communicable diseases epidemiology
etc.

21. Elaboration of epidemiology:
Term Explanation
StudyStudy Include: Surveillance, Observation,
Hypothesis testing, Research ,Research ,
and Experimentsand Experiments
Distributi
on
Refers to analysis of: Times, Persons,
and Places
DeterminantsDeterminants Include factors that influence health:
Genetic, Behavioral, Cultural,
Social, Physical, Economical,
Chemical and Biological
Last but not least Political and
Administrable

22. Elaboration of epidemiology:
continue
Term Explanation
Health-
related
states and
events
Refer to:CaCauses of Ill health, Diseasesuses of Ill health, Diseases
and Deathand Death and also on other hand
rreactions to preventive regimes andeactions to preventive regimes and
provision and use of health services.provision and use of health services.
SpecifiedSpecified
populationspopulations
Include: Identifiable characteristicsIdentifiable characteristics
viz. Occupational groups, HardcoreOccupational groups, Hardcore
populations etcpopulations etc
ApplicationApplication
toto
preventionprevention
As aim of Public Health_ to Promote ,Promote ,
Protect and restore health.Protect and restore health.

23. Hierarchy of study designsHierarchy of study designs

24. Health determinants, indicators, and risk
factors
Health determinants:
Health determinants are generally defined as the underlying social,
economic, cultural and environmental factors that are responsible for
health and disease, most of which are outside the health sector.
Health indicators:
A health indicator is a variable – that can be measured directly to
reflect the state of health of people within a community. WHO presents
the most recent data for 50 health indicators each year.25 Health
indicators can also be used as components in the calculation of a
broader social development index. The best example is the Human
Development Index, which ranks countries each year according to a
combination of the level of economic development, literacy, education,
and life expectancy (p://hdr.undp.org/).

25. Risk factors:
A risk factor refers to an aspect of personal habits or an
environmental exposure, that is associated with an increased
probability of occurrence of a disease. Since risk factors can
usually be modified, intervening to alter them in a favourable
direction can reduce the probability of occurrence of disease. The
impact of these interventions can be determined by repeated
measures using the same methods and definitions (as in Box)
Measuring risk factors:
Risk factors can include tobacco and alcohol use, diet, physical inactivity, blood pressure and obesity.
Risk factors can be used to predict future disease, their measurement at a population level is important &
challenging.
Tobacco use can be measured by self-reported exposure (yes/no), quantity of cigarettes smoked, or by
biological markers(serum cotinine).
Standardize methods of measurement of risk factors at the global level, including the WHO MONICA Project
in the 1980s and 1990s. WHO STEPS approach (Recent) to the measurement of population levels of risk
factors provides methods and materials to encourage countries to collect data in a standardized manner.
Note: Data from individual countries can be adjusted to account for known biases to make them
internationally comparable. This step is also necessary because countries conduct standard surveys at different
times. If risk factor rates are changing over time, information on trends will be needed to adjust data to a
standard reporting year.

26. Other specific(summary) Measures of population Health:
 Policy-makers face the challenge of responding to current disease prevention and
control priorities, while being responsible for predicting future priorities
 Decisions of policy-makers should be based on summary measures
 Summary measures serve as a common currency for reporting the burden of disease in
populations.
 Summary measures provide a way of monitoring and evaluating population health, so
that prevention and control actions can be taken rapidly when necessary.
 Mortality alone does not provide a full picture of how different causes affect population
health .
Population health summary measures:
I. Years of potential life lost (PLL) based on the years of life lost through premature death
(before an arbitrarily determined age);
II. Healthy life expectancy (HALE);
III. Disability-free life expectancy (DFLE);
IV. Quality-adjusted life years (QALYs);
V. Disability-adjusted life years (DALYs)

27. Types of epidemiological study DesignTypes of epidemiological study Design
Type of studyType of study Alternative nameAlternative name Unit of studyUnit of study
A) Observational
studies
1.Descriptive studies1.Descriptive studies
2.Analytical studies2.Analytical studies
Ecological studies
Cross-sectional studiesCross-sectional studies
Case-control studies
Cohort studiesCohort studies
-
Correlation studies
Prevalence studiesPrevalence studies
Case-reference studies
Follow-up studiesFollow-up studies
-
Population
IndividualsIndividuals
IIndividuals
IndividualsIndividuals
B).Experimental
studies
1.Randomized controlled1.Randomized controlled
trialstrials
2.Cluster randomized
controlled trials
3.Field trials3.Field trials
4.Community Trials
Intervention studies
Clinical trialsClinical trials
-
--
Community intervention
studies
IndividualsIndividuals
Groups
--
Healthy people of
communities

28. Applications of different observational study designsApplications of different observational study designs
objective Ecological Cross-sectional Case-control cohort
Investigation of rare disease ++++ --- +++++ ------
Investigation of rare cause ++ ---- ------ +++++
Testing Multiple effects of
cause
+ ++ ----- +++++
Study of multiple exposures
and determinants
++ ++ ++++ +++
Measurement of time
relationship
++ __ +b +++++
Direct measurement of
incidence
__ __ +c +++++
Investigation of long latent
periods
__ __ +++ __
+…+++++ indicates the general degree of suitability;there are exceptions
- Not suitable
B if prospective
C if population-based.

29. Control
(people without disease)
Not exposed
Not exposed
Start with:
Population
Exposed
Exposed
TimeTime
Direction of inquiry
Population
People
Without
Disease
Exposed
Not
exposed
Disease
Not disease
Disease
Not disease
Direction of inquiry
TimeTime
Design of a case-control studyDesign of a case-control study
Design of a cohort studyDesign of a cohort study

30. Population
People
with out
disease
Disease
No
disease
Cases
ControlsSample
Time (follow-up over many years)
Design of a Nested case-control studyDesign of a Nested case-control study

31. Population
Treatment
Intervention
RandomizationRandomization
No treatment
or Control or
Placebo group
Disease
No disease
Disease
No disease
Design of a Randomized controlled trialDesign of a Randomized controlled trial
Exclusions
The control &
subject will be
comparable at
the start of the
intervention
when the
randomization is
done properly
Matchin
g

32. Relative ability of different types
of study to “prove” causation
Type of study Ability to prove “causation
Randomized controlledRandomized controlled
trialstrials
Cohort studiesCohort studies
Case-control studiesCase-control studies
Cross-sectional studiesCross-sectional studies
Ecological studiesEcological studies
StrongStrong
ModerateModerate
ModerateModerate
WeakWeak
WeakWeak

33. Classification of Study Designs
Source: Grimes DA, Schulz KF. Lancet 2002; 359: 58

34. Potential Errors in Epidemiological studies:
Epidemiological investigations aim to provide accurate
measurement of disease occurrence ( or other outcomes) .
There many possibilities for errors in measurement.
Sources of error can be random or systematic.
Random error :
Random error is when a value of the sample measurement diverges –
due to chance alone – from that of the true population value. Random
error causes inaccurate measures of association. There are three major
sources of random error:
 Individual biological variation;
 Sampling error; and
 Measurement error
Note:Random error can never be completely eliminated since we can study only a
sample of the population

35.  Measurement error can be reduced by stringent protocols as
Sample size:
The sample size must be large enough for the study to have sufficient statistical
power to detect the differences deemed important. Sample size calculations can be
done with standard formulae as provided. The following information is needed
before the calculation can be done:
 Required level of statistical significance of the ability to detect a
difference
 Acceptable error, or chance of missing a real effect
 Magnitude of the effect under investigation
 Amount of disease in the population
 Relative sizes of the groups being compared
Note: In reality, sample size is often determined by logistic and financial considerations
and a compromise always has to be made between sample size and costs.

36. Systematic error:Systematic error:
The possible sources of systematic error in epidemiology are
many and varied; over 30 specific types of bias have been
identified. The principal biases are:
􀁸 selection bias
􀁸 measurement (or classification) bias.
Selection bias:
Selection bias occurs when there is a systematic difference
between the characteristics of the people selected for a study and
the characteristics of those who are not.
Example: If individuals entering or remaining in a study have
different characteristics from those who are not selected initially,
or who drop out before completion, the result is a biased
estimate of the association between exposure and outcome.

37. Measurement bias:
Measurement bias occurs when the individual measurements or
classifications of disease or exposure are inaccurate – that is, they do not
measure correctly what they are supposed to measure.
For instance:
 Biochemical or physiological measurements are never completely
accurate and different laboratories often produce different results
on the same specimen.
 A form of measurement bias of particular importance in
retrospective case control studies is known as recall bias.
 In ref. of measurement bias, If the investigator, laboratory technician or
the participant knows the exposure status, this knowledge can influence
measurements and cause observer bias . To avoid this bias, measurements
can be made in a blind or double-blind fashion. A blind study means that
the investigators do not know how participants are classified.
A double-blind study means that neither the investigators, nor the
participants, know how the latter are classified

38. Confounding:
 The word “Confounding” comes_Latin-confundere_mis together.
 Confounding can occur when another exposure exist in the study
population and is associated both with disease and the exposure being
studied
Confounding: Relationship between coffee drinkingcoffee drinking (as exposure), HeartHeart
diseasedisease (as outcome) and third variable(as tobacco usedtobacco used)
Confounding: Relationship between coffee drinkingcoffee drinking (as exposure), HeartHeart
diseasedisease (as outcome) and third variable(as tobacco usedtobacco used)
Coffee
drinking
(Exposure(Exposure
))
Heart
disease
((outcome)
Tobacco
use
(Confounding
variable)
Associated
to outcome,
Independent
exposure
Associated
with exposure
But not the
consequence of
exposure
Note: People who drink
coffee are more likely to
smoke than people who do
not drink coffee(Restriction)

39. Continue…
 Confounding is another major issue in epidemiological study and can have
a very important influence.
 Confounding arises because non-random distribution of risk factor in source
population also occurs in the study population thus providing misleading
estimates of effect and it might appear to be a bias ( not result from
systematic error in research design).
 Age and social class are often confounders in epidemiological studies.
The control of confounding: The methods commonly used
to control confounding in the design of an epidemiological study are:
􀁸 randomization
􀁸 restriction
􀁸 matching.
At the analysis stage, confounding can be controlled by:
􀁸 stratification
􀁸 statistical modeling.

40. Randomization:
 In experimental studies, randomization is the ideal
method for ensuring that potential confounding
variables are equally distributed among the groups
being compared.
 The sample sizes have to be sufficiently large to
avoid random mal distribution of such variables
Restriction:
One way to control confounding is to limit the study to
people who have particular characteristics. For
example, in a study on the effects of coffee on
coronary heart disease, participation in the study
could be restricted to nonsmokers, thus removing
any potential effect of confounding by cigarette
smoking.

41. Thank youThank you
for patiencefor patience
Many more parts of human epidemiology are with us