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3
Contents
Contents
Introduction
Introduction
History of epidemiology
History of epidemiology
Components of epidemiology
Components of epidemiology
Aims and objectives
Aims and objectives
Epidemiology v/s clinical medicine
Epidemiology v/s clinical medicine
Principles of epidemiology
Principles of epidemiology
Epidemiological approach
Epidemiological approach
Methods of epidemiology
Methods of epidemiology
Descriptive epidemiology
Descriptive epidemiology
Analytical epidemiology
Analytical epidemiology
Experimental epidemiology
Experimental epidemiology
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Association and Causation.
Association and Causation.
Dynamics of disease transmission
Dynamics of disease transmission
Disease prevention and control
Disease prevention and control
Investigation of an epidemic
Investigation of an epidemic
Conclusion
Conclusion
References.
References.
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INTRODUCTION
INTRODUCTION
I keep six honest serving men, they taught me all I know.
I keep six honest serving men, they taught me all I know.
Their names are
Their names are
what, when, why, how, where & who.
what, when, why, how, where & who.
When attempts are made to understand the cause of the
When attempts are made to understand the cause of the
diseases,
diseases, two general approaches may be considered.
two general approaches may be considered.
The first deals with the -
The first deals with the -
identification and tracing of the agent of the disease after
identification and tracing of the agent of the disease after
it has entered or affected the individual host & to this
it has entered or affected the individual host & to this
approach the term
approach the term ETIOLOGY
ETIOLOGY is used.
is used.
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The word
The word Etiology is derived from the Greek word
Etiology is derived from the Greek word
aitia = cause
aitia = cause
logos = description or science or study.
logos = description or science or study.
The second approach looks further, -
The second approach looks further, -
the
the patient is seen set in his environment
patient is seen set in his environment & as a part of
& as a part of
group of similar patients, human or otherwise, all reacting
group of similar patients, human or otherwise, all reacting
to the same disease.
to the same disease.
This broader field of study involves consideration of many
This broader field of study involves consideration of many
predisposing factors
predisposing factors to disease as well as apparent
to disease as well as apparent existing
existing
cause
cause & is thus concerned with the
& is thus concerned with the frequency of the disease
frequency of the disease
in the group.
in the group.
To this approach, study of the disease the term
To this approach, study of the disease the term
EPIDEMIOLOGY
EPIDEMIOLOGY is applied.
is applied.
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The word
The word EPIDEMIOLOGY
EPIDEMIOLOGY is derived from
is derived from
the Greek word, Epidemic,
the Greek word, Epidemic,
Epi
Epi = upon,
= upon,
demos
demos = people,
= people,
logos
logos = science or study.
= science or study.
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HISTORY
HISTORY
Adam and eve The story of forbidden fruit
Adam and eve The story of forbidden fruit
Hippocrates(460 375 BC ) was the first known
Hippocrates(460 375 BC ) was the first known
epidemiologist.
epidemiologist.
No disease is sent by evils or demons, but is
No disease is sent by evils or demons, but is
the result of natural causes-
the result of natural causes-
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Thomas syndenham
Thomas syndenham (1624 - 1689): wrote the history of
(1624 - 1689): wrote the history of
disease and became the
disease and became the founder of epidemiology.
founder of epidemiology.
John snow (1813- 1858):
John snow (1813- 1858): is considered the
is considered the
father of epidemiology
father of epidemiology
epidemic of cholera in London, in
epidemic of cholera in London, in
August 1854.
August 1854.
William budd
William budd (1811 - 1880): studied the typhoid.
(1811 - 1880): studied the typhoid.
Foundation of epidemiology was laid down in 19
Foundation of epidemiology was laid down in 19th
th
century.
century.
Winslow and Sedgwick
Winslow and Sedgwick lectured epidemiology in 1920.
lectured epidemiology in 1920.
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10
W.H Frost
W.H Frost became the
became the first professor of
first professor of
epidemiology in 1927.
epidemiology in 1927.
In 1941, Mc Alistair Gregg through
In 1941, Mc Alistair Gregg through
epidemiologic study proved rubella and
epidemiologic study proved rubella and
congenital cataract.
congenital cataract.
R.doll and A. Bradford hill (1950, 1964): smoking
R.doll and A. Bradford hill (1950, 1964): smoking
and carcinoma of lung.
and carcinoma of lung.
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DEFINITIONS OF EPIDEMIOLOGY
DEFINITIONS OF EPIDEMIOLOGY
PARKIN
PARKIN (1873) defines epidemiology as the branch of
(1873) defines epidemiology as the branch of
medical science which deals with the treatment of
medical science which deals with the treatment of
epidemics.
epidemics.
Mac Mohan and Pugh(1960):
Mac Mohan and Pugh(1960):
Defines epidemiology as the study of the distribution
Defines epidemiology as the study of the distribution
and determinants of disease frequencies in man.
and determinants of disease frequencies in man.
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AMERICAN EPIDEMIOLOGICAL SOCIETY
AMERICAN EPIDEMIOLOGICAL SOCIETY
the science which concerns itself with the natural
the science which concerns itself with the natural
history of disease as it is expressed in groups of persons
history of disease as it is expressed in groups of persons
related by some common factors
related by some common factors of age, sex, race,
of age, sex, race,
location or occupation
location or occupation as distinct from development of
as distinct from development of
disease in individuals.
disease in individuals.
JOHN M LAST (1988)
JOHN M LAST (1988)
Epidemiology is the study of the distribution and
Epidemiology is the study of the distribution and
determinants of health-related states or events in
determinants of health-related states or events in
specified populations, and the application of this study
specified populations, and the application of this study
to the control of health problems.
to the control of health problems.
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Components of epidemiology
Components of epidemiology
Disease Frequency:
Disease Frequency:
Basic measures rate and ratio
Basic measures rate and ratio
Facilitates comparison subgroups/ populations ----
Facilitates comparison subgroups/ populations ----
etiology ----- prevention or control of disease. (Statistics)
etiology ----- prevention or control of disease. (Statistics)
Studies of Distribution:
Studies of Distribution:
Disease occurs in patterns
Disease occurs in patterns
Distribution patterns by time, place & person
Distribution patterns by time, place & person
(descriptive)
(descriptive)
Generate hypothesis.
Generate hypothesis.
14. Studies of Determinants:
Studies of Determinants:
To identify the underlying causes or risk factors.
To identify the underlying causes or risk factors.
Analytical studies
Analytical studies
Help in developing scientifically sound health
Help in developing scientifically sound health
programmes, interventions, and policies.
programmes, interventions, and policies.
Helped in understanding the determinants of
Helped in understanding the determinants of
chronic diseases e.g. lung cancer, CVD.
chronic diseases e.g. lung cancer, CVD.
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Aims of epidemiology
Aims of epidemiology
As stated by International Epidemiologic Association
As stated by International Epidemiologic Association
( IEA ).
( IEA ).
To describe the magnitude and distribution of the
To describe the magnitude and distribution of the
disease problem in human populations.
disease problem in human populations.
To provide data essential for planning, implementation,
To provide data essential for planning, implementation,
and evaluation of health services and setting priorities
and evaluation of health services and setting priorities
among the services.
among the services.
To identify risk factor or etiological agents.
To identify risk factor or etiological agents.
The ultimate aim of epidemiology is
The ultimate aim of epidemiology is
To eliminate or reduce the health problem or its
To eliminate or reduce the health problem or its
consequences and
consequences and
To promote the health and well being of society as a
To promote the health and well being of society as a
whole.
whole.
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SL
NO
EPIDEMIOLOGY CLINICAL MEDICINE
1. Unit of study -- Defined
population / popu. at risk .
Individual/case.
2. Relevant data, identifies
sources of infection, mode of
spread, determines future
trends & control measures.
Case, diagnosis, prognosis,
prescribes treatment.
3. Concerned with those who
are sick & those who are
healthy
Often concerned with those
who are sick.
4. Investigator goes to
community
Patients comes to doctor
5. Conceptual, results in the
form of tables & graphs.
Based on biomedical
concepts, refining tech..of
diagnosis & treatment at ind.
level.
17. Clinician ---interested in cases with
disease
Statistician --- population from which
cases are derived
Epidemiologist ---- the relationship
between cases and the population in the
form of rate.
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Principles of epidemiology
Principles of epidemiology
Exact observation
Exact observation
Correct interpretation
Correct interpretation
Rationale explanation
Rationale explanation
Scientific construction
Scientific construction
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Epidemiological approach
Epidemiological approach
Asking questions Making comparisons
Reltd to health events.
What is the event
What is its magnitude
Where did it happen
When did it happen
Who are affected
Why did it happen
Relatd to health action
What can be done
How can it be prevented in future
what action sh taken by comm, health
services, other sectors, where and whom
services carried out
What resources are required
How activities are to be organized
What difficulties may arise and how to over
come.
20. Comparability ( in age, sex,& other pertinent
variables)
Matching (done for selected characteristics that
might confound the interpretations of the results )
Standardization ( limited to age sex and parity )
MAKING COMPARISIONS
21. Basic measurement in epidemiology
Definition of What is to be measured
Criteria by which it can be measured
1.Acceptable
and
applicable
2.Precise
and valid
3. Clear
Measure in
epidemiology
Mortality
Morbidity
Natality
Presence or absence of
characteristic attributes of
disease.
Medical needs, health
care facilities, utilization
of health services, others
Environmental factors
Demographic variables.
Requirements.
Validity
Reliability
Accuracy
Sensitivity
Specificity
Tools of measurements
Rates
Ratios
Proportions
22. Tools of measurment
It measures the development of
particular event in a population at given
period of time.
Risk of developing a condition.
It indicates change in some event.
Rates
Death rate:
No. of deaths in one year
Mid- year population
Various categories of rates:
1. Crude rates (unstandardized rates)
2. Specific rates.
3. Standardized rates
1000
23. Ratio
It expresses a relation in size between
the random quantities.
Numerator is not a component of
denominator.
Numerator and denominator involve
the time interval.
WBCS: RBCS 1:600
X:Y or x / y
Sex ratio, doctor population ratio.
Proportion
Is a ratio which indicates the relation in magnitude
of a part of the whole.
Numerator is always included in the denominator.
No of children scabies at certain time
x100
Total no of children in that village at the same
time
24. Concept of numerator and denominator
Concept of numerator and denominator
The numerator and denominator of a rate should be similarly
restricted
Numerator
Refers to number of times an event has occurred in a
population
It is a part of denominator in rate and proportion, but not
in ratio
Denominator
Numerator has little meaning, unless accompanied by
denominator
epidemiologist has to choose an appropriate denominator
while calculating a rate.
Denominator may be related to
Population
Total events taken place
25. Denominator related to population
Denominator related to population
Mid year population
Mid year population
Population estimated to be present as on the first day
of July every year.
Population at risk
Population at risk
Person- Time
Person- Time
Eg. Person- years
Person- Distance
Person- Distance
Eg. Passenger- miles
Sub groups of the population
Sub groups of the population
Eg. Age groups, sex groups, professional groups, etc.
26. Denominator related to events
Denominator related to events
In some cases, the denominator may be related
to the events, instead of population
Eg.
.
Annual rate of motor vehicle accidents
Number of accidents in one year
Number of accidents in one year
Vehicle-
miles
X 1000
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STANDARDIZED RATES:
STANDARDIZED RATES:
The overall rates adjusted for the effects of
The overall rates adjusted for the effects of
differences in population
differences in population
Composition, such as in age, sex etc.
Composition, such as in age, sex etc.
For comparison between two populations
For comparison between two populations
with different compositions
with different compositions
Direct standardization
Direct standardization
Indirect standardization.
Indirect standardization.
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Incidence and Prevalence
Incidence and Prevalence
Incidence
Incidence it is defined as the number of
it is defined as the number of
new cases occurring in a defined population
new cases occurring in a defined population
during a specified period of time.
during a specified period of time.
Number of new cases of specific disease during
Number of new cases of specific disease during in
in
a defined population during a given time period
a defined population during a given time period
Population risk at that period
Population risk at that period
*1000
*1000
29. Incidence rate refers to
Incidence rate refers to
Only to new cases
Only to new cases
During a given period (usually one
During a given period (usually one
year)
year)
Population at risk
Population at risk
Also refers to spells of diseases
Also refers to spells of diseases
arising.
arising.
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29
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Special incidence rates
Special incidence rates
A)
A) Attack rate
Attack rate
An attack rate is an incidence rate usually
An attack rate is an incidence rate usually
expressed in percentage, used only when the
expressed in percentage, used only when the
population is
population is exposed to risk for a limited period of
exposed to risk for a limited period of
time such as during epidemic.
time such as during epidemic.
B)
B) Secondary attack rate
Secondary attack rate
Defined as the of exposed persons developing the
Defined as the of exposed persons developing the
disease
disease within the range of the incubation period
within the range of the incubation period
following exposure to a primary case.
following exposure to a primary case.
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Uses of incidence rates
Uses of incidence rates
Helps in taking action to
Helps in taking action to control the disease.
control the disease.
Give clues to
Give clues to research into etiology and
research into etiology and
pathogenesis of disease.
pathogenesis of disease.
Helps in the study of
Helps in the study of distribution of disease.
distribution of disease.
Useful in
Useful in evaluating the efficacy of
evaluating the efficacy of
preventive and therapeutic measures.
preventive and therapeutic measures.
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Prevalence
Prevalence
No. of cases
No. of cases (both old and new)
(both old and new) in a defined population
in a defined population
at a specified point in time or over a period of time in a
at a specified point in time or over a period of time in a
given population.
given population.
PREVALENCE RATE (P):
PREVALENCE RATE (P):
Expressed as cases per 100 population
Expressed as cases per 100 population
Types of prevalence
Types of prevalence
Point prevalence
Point prevalence
Period prevalence
Period prevalence
No. of all current cases of a specific disease at one
No. of all current cases of a specific disease at one
point in time in relation to a defined population
point in time in relation to a defined population
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Point prevalence rate.
Point prevalence rate.
Period prevalence
Period prevalence
It is a measure that expresses total no. of cases of a
It is a measure that expresses total no. of cases of a
disease known to have existed at some time during a
disease known to have existed at some time during a
specified period
specified period
Total no. of all current cases of a
Specified disease existing at a given point of time
Estimated population at
the same point in time
X100
Total no. of all current cases of a Specified
disease at a given period of time interval
Estimated mid- interval population at risk
X100
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Uses of prevalence rate
Uses of prevalence rate
In detecting the magnitude of disease in
In detecting the magnitude of disease in
the community
the community
In identifying potential high risk
In identifying potential high risk
populations
populations
In administrative and planning
In administrative and planning
purposes like, assessing manpower
purposes like, assessing manpower
needs in health services, delivery of
needs in health services, delivery of
health services etc.
health services etc.
35. Limitations of prevalence rate
Limitations of prevalence rate
Not the ideal measure for studying
Not the ideal measure for studying
etiology
etiology
Depends up on incidence and
Depends up on incidence and
duration
duration
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35
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Relation b/w prevalence and incidence
Relation b/w prevalence and incidence
Prevalence rate is dependent on both incidence
Prevalence rate is dependent on both incidence
rate and disease duration.
rate and disease duration.
Assuming that the population is stable, the
Assuming that the population is stable, the
incidence value and the duration is unchanging,
incidence value and the duration is unchanging,
a relationship can be established as
a relationship can be established as
Prevalence = Incidence x Avg. duration disease.
P = I X D
