This document discusses epidemiological methods for studying the distribution and determinants of health events and applying that knowledge to disease control. It defines descriptive epidemiology as the study of disease occurrence, distribution, and patterns in populations. Descriptive methods are observational and can be cross-sectional or longitudinal. Descriptive epidemiology provides insights into disease frequency, trends, and risk factors to inform public health planning and resource allocation.

1. Methods
Study of distribution and determinants of health related events and its
application to control health problems.
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2.  Enumerate two different types of epidemiological
methods .
 To define descriptive epidemiology and describe
importance of time, place and person
distribution.
 Enumerate three kinds of time fluctuations in
disease occurrence.
 To describe disease load in terms of prevalence
and incidence.
 To differentiate cross sectional and longitudinal
studies.
 To enumerate two used of descriptive
epidemiology.
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3. Dynamic study of the
Determinants
Occurrence
Distribution
Control
Pattern
Of health and disease in a population
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4.  Is the basic science of public health
 Provides insight regarding the nature, causes,
and extent of health and disease
 Provides information needed to plan and
target resources appropriately
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5.  Measures of frequency
◦ Counts and rates
 Measures of association
◦ Relative risk
◦ Odds ratio
 Statistical inference
◦ P-value
◦ Confidence limits
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6.  Observational studies- Investigator only
measures. Does not interfere.
--Descriptive studies.
--Analytical studies .
 Experimental studies. Also called Interventional
studies. – Active attempt by investigator.
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7. Descriptive
Analytic
Experimental
Further studies to determine the
validity of a hypothesis concerning
the occurrence of disease.
Deliberate manipulation of the
cause is predictably followed
by an alteration in the effect
not due to chance
Study of the occurrence and
distribution of disease
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8. Descriptive
 Used when little is
known about the
disease
 Rely on preexisting
data
 Who, where, when
 Illustrates potential
associations
Analytic
 Used when insight about
various aspects of
disease is available
 Rely on development of
new data
 Why
 Evaluates the causality of
associations
Both are important!
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9.  Observation on population or individual.
(dengue in gokula ).
 Time distribution- When disease occurring?
 Place distribution- Where ?
 Person –Who is getting it ?
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10.  1. Defining population-Whole population in a
geographic area, or representative
population. Should be large enough. Age,
sex, occupation and other information. Also
called Population at Risk. Framingham study !
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11.  2. Disease under study-Precise with validity.
Well defined diagnostic method acceptable to
the population. If not defined precisely, it
leads to errors.
Operational definition of the disease. Once
accepted, it cannot be changed.
Example- Dengue.
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12.  Disease is seasonal, ? Periodic fluctuation ?
 Short term fluctuation – EPIDEMIC .-
’’Occurrence in a community of illness or
event clearly in excess of normal expectancy.”
 Periodic fluctuation
 Long term trends-
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13.  Endemic - The habitual presence (or usual occurrence) of a
disease within a given geographic area
 Epidemic - The occurrence of an infectious disease clearly in
excess of normal expectancy, and generated from a common
or propagated source
 Pandemic - A worldwide epidemic affecting an exceptionally
high proportion of the global population
Number
of Cases
of
Disease
Time 13IMS BANGALORE

14.  Common source epidemic- 1.Point source-
brief exposure, epidemic is severe, all case in
one incubation period. –Food poisoning.
2. Continuous or repeated exposure-
Gonorrhea, respiratory infection, water
contamination.
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15.  Infectious, Person to person.
 Gradual rise, fall over a long period.
 Long term transmission. Herd immunity ?
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16.  Seasonal trend, -Measles, URTI, Diarrhea,.
 Cyclic trend- Influenza (H1N1).
 Long term trends- CVD, Tuberculosis,
NIDDM.
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17.  Geographical variation- environment, diet, etc.
 International variation- Ca stomach (Japan Vs
USA ) , Ca Oral cavity (India )
 National variation – Malaria –Sabah , Sarawak.
Filariasis- Perak, Sabah.
 Migration studies- Tuberculosis among
migrants in Malaysia.
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18. Age Hobbies
Sex Pets
Occupation Travel
Immunization status Personal Habits
Underlying disease Stress
Medication Family unit
Nutritional status School
Socioeconomic factors Genetics
Crowding Religion
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19.  Disease load in a population.
 Mortality, Morbidity, Disability .
 Morbidity- Incidence, Prevalence.
 Prevalence- All current cases existing at a
given point of time in a given population.
 Incidence- Number of NEW cases occurring in
a defined population during a specific time.
 How to measure ?
 Hypothesis.
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20.  Morbidity: Refers to the presence of disease
in a population
 Mortality: Refers to the occurrence of death in
a population
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21.  Prevalence is the number of existing cases
of disease in the population during a defined
period.
 Incidence is the number of new cases of
disease that develop in the population during
a defined period.
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22. Prevalence: The number of existing cases in
the population during a given time period.
PR = # existing cases during time period
population at same point in time
Prevalence rates are often expressed as a
percentage.
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23.  Population denominator:
IR = # new cases during time period X K
specified population at risk
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24. During a six-month time period, a total of 53
nosocomial infections were recorded by an
infection control nurse at a community
hospital. During this time, there were 832
patients with a total of 1,290 patient days.
What is the rate of nosocomial infections
per 100 patient days?
IR =
53 X 100
1,290 pt. days
=
4.1 infections per
100 pt. days
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25.  An educated guess
 an unproven idea
 based on observation or reasoning, that can
be proven or disproven through investigation.
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26.  Cross sectional-
Single examination
of a cross section
of population.
Prevalence study.
 Longitudinal
Repeated
observation in the
same population.
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27.  trends in health and disease and allow
comparisons among countries and
subgroups within countries
 Provides clue to disease etiology.
 provides a basis for planning, provision and
evaluation of services
 identifies problems to be studied by
analytic methods (?)and to test hypotheses
related to those problems
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28. 28IMS BANGALORE

29. . Circle the most appropriate explanation on “Prevalence rate”:
a. the number of patients who have the disease at a particular time,
divided by the population at risk of having the disease at that
time.
b. the number of new cases of a diseased in a population over a
period of time.
c. not useful for developing HIV/AIDS control programme.
d. useful for developing Avian flu control programme.
e. not useful for any disease control programme.
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30.  What is Epidemic ?
 What is endemic ?
 What is pandemic ?
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31.  1. Define population
 2. Define the disease
 3. Randomized trial
 4. Measurement of a disease.
 5. Formulate an hypothesis.
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