1. 8 Community Medicine
Principle of Epidemiology 11
Methods of Epidemiology
Dr. Siham Gritly
University of Bahri
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2. Dr. Siham Gritly 2
Epidemiologic methods are used for the identification of risk
factors for disease and determination of optimal treatment
approaches used in clinical practice

3. Methods of Epidemiology
• Epidemiologic methods are used for;
• -the identification of risk factors for
disease
• -and determination of optimal treatment
approaches used in clinical practice.
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4. • In the study of communicable and chronic
diseases, the work of epidemiologists
involves;
• study design,
• data collection
• and statistical analysis
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5. Epidemiological studies classified in two
categories
• 1-observational studies (non experimental
studies)
• A) descriptive studies
• B) Analytical studies
• 2-experimental studies (intervention studies)
• A) Randomized Controlled trial or clinical trail
• B) 2-non randomized or non-experimental trials
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6. 1-observational studies
• researcher observes association between
exposure and disease, estimates and tests it
• 1-observational studies Include;
• A) descriptive studies
• B) Analytical studies
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7. A) descriptive studies
• Descriptive studies are usually the first phase
of an epidemiological investigation
• Observing the distribution of disease or health
related characteristics in human population
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8. • In Descriptive studies questions should be
asked such as;
• When is the disease occurring----time
distribution
• Where it is occurring------place distribution
• Who is getting the disease----persons
distribution
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9. Procedures in Descriptive studies
• 1-defining the population to be studied
• 2-defing disease under study
• 3-describing the disease by;
• -time
• Place
• Person
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10. • 4-measurement of disease
• 5-comparing with known indices
• 6-formulation of an aetiological
hypothesis
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11. • 1-defining the population to be studied
• Descriptive study are investigation of
population not individual; include total number
• Sex
• Age
• Occupation
• cultural
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12. • 2-defing disease under study;
• Specified the disease to be investigated
• The main objective to obtain accurate
estimate of disease in a population
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13. • 3-describing the disease by;
• The main primary objective of descriptive
epidemiology is to describe the occurrence and
distribution of disease by
• Time--
• Place
• person
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14. • 4-measurement of disease
• The information should be available in terms
of
• Mortality
• Morbidity (incidence and prevalence)
• distribution
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15. • 5-comparing with known indices
• Making comparisons between different
population, this is to ; identify groups who are
at risk for certain diseases
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16. • 6-formulation of an aetiological hypothesis
• Hypothesis should formulated in a manner that
that it can be tested
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17. • Hypothesis should specify the following
• -the population- the characteristics of the
persons to whom the hypothesis to be applied
• -the specific cause being considered
• -the expected outcome
• -the dose-response relationship
• -the time-response relationship (time between
exposure to the cause observed)
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18. B) Analytical studies
• Analytical studies are the second major type of
epidemiological studies
• In contrast to descriptive studies which look for
the whole population the analytical studies look
for individual within the population
• Main types of observational studies are;
• Case control study
• Cohort study
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19. Cohort or follow up
cohort study (prospective) ;
-individual exposed to particular factors
Presence or absence
of particular diseaseIndividual unexposed to particular
factors
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Typical analytical study designs:
Cohort or follow up with individual as a unit of
study. An example ; investigation of a cohort of
smokers and non-smokers over time to estimate
the incidence of lung cancer (prospective) ;

20. case-control or case-references
Cases (disease
present)
Control (disease
absent)
Suspected or risk
factors
Individuals with
particular disease
Individual without
particular disease
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case-control or case-references with
individual as a unit of study
select subjects based on their disease status. It
is a retrospective study.
-factors present or absent---Observational

21. • Cross-sectional or prevalence with individual
as a unit of study
• Ecological or correlation with population as
unit of study
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22. Dr. Siham Gritly 22

23. 2-experimental studies or
Interventional:
• Experimental studies are of two types
• A-Randomized Controlled trial or clinical trail
• B-non randomized or non-experimental trials
• -field trials or community intervention studies
• -Community trial
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24. A)-Randomized Controlled trial or clinical
trail
• A study design that randomly assigns
participants into an experimental group or a
control group.
• As the study is conducted, the only expected
difference between the control and
experimental groups in a randomized
controlled trial (RCT) is the outcome variable
being studied.
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25. • Design of randomized control trial;
• The protocol;
• Selecting reference and experimental population
(make necessary exclusions)
• Randomize of two
• 1-experimental group
• 2-control group
• Follow up
• assessment
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26. • Advantages
• No population bias
• Results can be analyzed with well known
statistical tools
• Populations of participating individuals are
clearly identified
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27. • Disadvantages
• Expensive in terms of time and money
• biases: the population that participates may not be
representative of the whole
• Does not reveal causation
• Loss to follow-up
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28. B-Non-randomized controlled trial
• An experimental study in which people are
allocated to different interventions using
methods that are not random.
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29. Study Designs: Types
• Qualitative
• Quantitative
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30. Qualitative Quantitative
Definition a systematic
subjective
approach used to
describe life
experiences and give
them meaning
a formal, objective,
systematic process for
obtaining information about
the world. A method used to
describe, test relationships,
and examine cause and
effect relationships.
Goals To gain insight;
explore the depth,
richness, and
complexity inherent
in the phenomenon.
To test relationships,
describe, examine cause
and effect relations
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31. Qualitative Quantitative
Characteristic
•Soft science
•Focus: complex &
broad
•Subjective
•Basis of knowing:
meaning & discovery
•Develops theory
•Shared interpretation
•Communication &
observation
•Basic element of
analysis: words
•Individual
interpretation
Hard science
Focus: concise & narrow
Objective
Basis of knowing:
cause & effect,
relationships
Tests theory
Control
Instruments
Basic element of
analysis: numbers
Statistical analysis
GeneralizationDr. Siham Gritly 31

32. Objective vs Subjective
• Objective is a statement that is completely
unbiased.
• It is confirmable by looking up facts or
performing mathematical calculations.
• scientific facts are objective as are
mathematical proofs; essentially anything
that can be backed up with solid data.
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33. • Subjective is a statement that has been colored
by the character of the speaker or writer.
• It often has a basis in reality,
• It cannot be verified using concrete facts and
figures
• Subjective : opinions, interpretations, and any
type of marketing presentation are all subjective.
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34. references
• Park's Textbook of Preventive and Social
Medicine 21 Edition, by K. PARK
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