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SEMINAR
EPIDEMIOLOGYDEFINITION , SCOPE ,APPROACH ,MEASUREMENTS
Presented by:
Dr Nikita Sharma
Assisstant Professor
Dept .of Community
Medicine,MGMCH,Jaipur
Epidemiology is the basic science of Preventive
and Social Medicine.
• Epidemiology is scientific discipline of public
health to study diseases in the community to
acquire knowledge for health care of the society.
(prevention, control and treatment).
Epidemiological principles and methods are applied in
–
- Clinical research,
- Disease prevention,
- Health promotion,
- Health protection and
- Health services research.
• The results of epidemiological studies are also used
by other scientists, including health economists, health
policy analysts, and health services managers.
DEFINITION
“The study of the distribution and determinants of health-
related states or events in specified populations, and the
application of this study to the prevention and control of
health problems”
As defined by John M. Last (1988)
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DISTRIBUTION
• Distribution of disease occurs in a PATTERN.
• PATTERN- Time, Place, Person
. • PATTERN – Hypothesis for Causative/Risk factor –
Etiological Hypothesis. • Descriptive Epidemiology.
PERSON
• AGE
• SEX
• RACE
• SOCIO ECONOMIC STATUS
• RESIDENCE
• MARITAL STATUS
• OCCUPATION
BIMODALITY
There may be two separate peaks instead of
one in the age incidence curve of a disease.
This is known as bimodality as seen in
Hodgkin’s lymphoma, breast cancer.
It indicates that there are two different sets of
causative factors even though the clinical and
pathological manifestations of the disease is
the same in all ages
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PLACE
• International
• National
• Urban/rural difference
• Localised pattern of disease
MIGRATION STUDIES
The use of migrant studies is a way of distinguishing
genetic and environmental factors.
Carried out in 2 ways-
1) Study of genetically similar groups but living
under different environmental conditions. Eg: Twins
2) Study of genetically different groups living in a
similar environment.
Eg: Men of Japanese origin living in USA have higher
rate of coronary heart disease than the Japanese in
Japan
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COMMON SOURCE EPIDEMICS
1) Single exposure-
It can occur due to an infectious agent or as a result of
contamination of the environment and develops within
one incubation period.
Eg: Bhopal gas tragedy, Minamata disease
The epidemic curve rises and falls rapidly, usually has
one peak
It tends to be explosive (i.e. clustering of cases within a
short time)
CONTINUOUS EXPOSURE
It is when the exposure from the same source is
prolonged and the epidemic continues over more than
one incubation period.
The epidemic reaches a sharp peak, but tails off
gradually over a longer period of time.
Eg: A well of contaminated water or nationally
distributed vaccine(polio vaccine) or food; water borne
cholera.
PROPAGATED EPIDEMICS
Types- person to person, arthropod, animal
The epidemic shows gradual rise and tails
off over a much longer period of time
It is more likely to occur where there is
i) regular supply of new susceptible
individuals- Births, Immigrants
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PERIODIC FLUCTUATIONS
1) Seasonal trend- Seasonal variation is
characteristic of many communicable diseases.
Eg: Measles, upper respiratory tract
infections(seasonal rise during winter), Malaria,
etc.
Non-infectious diseases and conditions may
sometimes exhibit seasonal variation.
Eg: Sunstroke, hay fever.
2) Cyclic trend- Some diseases occur in cycles
spread over short periods of time (days, weeks,
months or years) .
Eg:
Influenza pandemics are known to occur at
intervals of 7-10yrs due to antigenic variations.
Non-infectious conditions may also occur in this
trend. Eg: Automobile accidents in the US are
more frequent on weekends.
C) LONG TERM TRENDS /SECULAR
TRENDS
It refers to changes in the occurrence of
disease over a long period of time.
Eg: Coronary disease, diabetes showing
consistent upward trend and
a decline in TB, polio in developed countries
during the past 50 yrs.
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DETERMINANTS
• Identifying the causes and risk factors for diseases.
• Testing the Hypothesis
• Analytical Epidemiology
SCOPE OF EPIDEMIOLOGY
1. Causation of the disease.
• 2. Natural history of the disease.
• 3. Health status of the population.
• 4. Evaluation of Interventions.
CAUSATION OF THE DISEASE.
• Most of diseases are caused by interaction
between genetic and environmental factors.
(Diabetes)
• Personal behaviors affect this interplay.
• Epidemiology is used to study their influence
and the effects of preventive interventions
through health promotion.
EPIDEMIOLOGICAL TRIAD OF TBA cause of a disease is an event,
condition, characteristic, or
combination of these factors which plays
an important role in producing the
disease. •
A cause could be sufficient
or necessary
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HEALTH STATUS OF THE POPULATION
• Epidemiology is often used to describe the
health status of population.
• Knowledge of the disease burden in
populations is essential for health
authorities.
• To use limited resources to the best possible
effect by identifying priority health
programmes for prevention and care.
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EVALUATION OF INTERVENTIONS
• To evaluate the effectiveness and efficiency of health
services.
• This means determining things such as – -
- Impact of Contraceptive use on Population Control.
- -the efficiency of sanitation measures to control
diarrheal diseases and
- the impact of reducing lead additives in petrol.
EPIDEMIOLOGIC APPROACH
1. Identify a PROBLEM –determine the extent and
magnitude of problem
2. Formulate a HYPOTHESIS ( asking the right
question ) ; ; good hypotheses are: Specific, Measurable,
and Plausible
3. TEST that HYPOTHESIS( assumptions vs. type
of data )
4. always Question the VALIDITY of the result(s) :
: Chance ; Bias
Asking questions Related to Health Events
. What is the event? (Problem)
2. What is magnitude?
3. Where did happen?
4. When did happen?
5. Who are affected?
6. Why did it happen?
Related to Health Action
1. What can be done to reduce the problem?
2. How can be prevented in future?
3. What action should be taken by community?
4. What resources required?
5. How activities to be organized?
6. What difficulties may arise?
Epidemiology is “a means of learning by asking questions
and getting answers that lead to further questions.”
TOOLS OF MEASUREMENTS
Basic tools are –
• 1. Rate
• 2. Ratio
• 3. Proportion
• Used for expression of disease magnitude.
RATE
• A “Rate” measures the occurrence of some
specific event in a population during given
time period.
• Example
Death Rate = total no of death in 1 yr / Mid-
year population x 1000.
ELEMENTS – Numerator, Denominator,
time & multiplier.
CATEGORIES OF RATE
A)CRUDE RATE- These are the actual observed
rates such as birth and death rates. Crude rates are
also known as unstandardized rates.
B) SPECIFIC RATES –These are actual observed
rates due to :
specific causes(e.g Tuberculosis) or
occuring in specific group(eg. Age, sex groups)
or during specific time period
(eg. Annualy , monthly ,weekly)
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STANDARDIZE RATES-These are
obtained by direct or indirect method of
standardization or adjustment . Eg. Age
and sex standardized rate
RATIO
• Ratio measures the relationship of size of two
random quantities.
• Numerator is not component of denominator.
• Ratio = x / y
Example-
- Sex – Ratio
- Doctor Population Ratio.
PROPORTION
• Proportion is ratio which indicates the
relation in a magnitude of a part of whole.
• The Numerator is always part of
Denominator.
• Usually expressed in percentage.
NUMERATOR AND DENOMINATOR
• Numerator – Number of times an event has
occurred in a population during specified time
period . (sickness, birth)
• Denominator –
1.Total population - Mid-year population -
Population at risk
2. Total events
MEASURING DISEASE FREQUENCY
INCIDENCE AND PREVALENCE
• These are fundamentally different ways of
measuring disease frequency.
• The incidence of disease represents the
rate of occurrence of new cases arising in a
given period in a specified population, while
• prevalence is the number of existing
cases (old+ new) in a defined population at a
given point in time
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INCIDENCE
“Number of new cases occurring in
defined population during specified period
of time”
• Incidence = Number of new cases
during given period / Population at risk x
1000
PREVALENCE
• Prevalence is total no of existing
cases ( old + new) in a defined
population at a particular point in time
or specified period.
• Prevalence = Total no of cases at
given point of time / Estimated
population at specified time x 100
RELATION BETWEEN INCIDENCE &
PREVALENCE
Prevalence = Incidence x Mean duration of d/se.
P = I x D
Example – if, I= 10 cases per 1000 per year.
D = 5 years.
P = 10 x 5
That is 50 cases per 1000 population
1. Point Prevalence
Prevalence for given point of time. •
2. Period Prevalence
Prevalence for specified period.
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SCOPE OF MEASUREMENTS IN
EPIDEMIOLOGY
MEASUREMENTS IN EPIDEMIOLOGY
1. Measurement of mortality.
2. Measurement of morbidity.
3. Measurement of disability.
4. Measurement of natality.
5. Measurement of presence or absence of attributes.
6. Measurement of health care need.
7. Measurement of environmental & other risk
factors.
8. Measurement of demographic variables.
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