The document provides an overview of analytic studies in epidemiology, focusing on cohort and case-control study designs. Cohort studies follow two groups (exposed and non-exposed) over time to assess health outcomes, while case-control studies compare groups with and without outcomes to analyze past exposures. Each study design has its advantages and disadvantages related to data collection, cost, time, and potential biases.

1. ANALYTIC STUDIES
Prepared By:
Dr.Anees AlSaadi
CMT-P R4
December 2013

2. ANALYTIC STUDIES
• OUTLINE:
– Hierarchy of Study design.
– Introduction for analytic Studies./ Exposure &
Outcome.
– Cohort and Case control Study design:
• Definition.
• Character.
• Advantages and disadvantages.

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Introduction

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Introduction:
Testing specific hypotheses.
Samples of subjects are identified and information
about exposure status and outcome is collected.

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Introduction:
Groups of subjects are compared in order to estimate
the magnitude of association between exposures and
outcomes.

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Introduction:
The two main types:
Cohort study
Case-control study

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Introduction:
Exposure
Outcome

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Cohort study:
Exposure
Outcome

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Cohort study:
Definition

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Cohort study:
Definition

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Cohort study:
Definition
Is an analytic epidemiologic research design in
.which the study population is composed of
individuals who are classified as exposed and no
exposed to particular risk factors. These groups are
followed forward for a specific period of time to
estimate the incidence rate of an outcome or the
development of a health problem.

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Non Exposed
Group
Hypothesized to be at
greater risk or lesser risk
of developing the health
problem
Exposed Group
Cohort study:
Already
exposed.
Casual factors
Protective
factors
Not exposed
Protective
factors
Casual factors

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Cohort study:
What is the Potential Source of Study
Subjects…… ?

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Cohort study:
Developing
problem.
Not
developing
problem.
Death.
Study Subjects
in Each Groups
followed in same
manner.
Lost to
follow up.
Study
Ends.

15. ANALYTIC STUDIES
Cohort study:
Cohort study
Prospective
Historical
Exposure status is
determined when the
study begins.
Followed forward in
time to observe the
outcome.
The exposure happened
before the study begins.

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Cohort study:
Example

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Cohort study:
The most important bias is loss of
follow ups (drop out).

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Cohort study:
•
•
•
•
•
•
Advantages:
More control on data
collection.
Easy checking the study
outcome.
Clear temporal sequence.
Estimating the risk.
Good to study rare risk factors.
Can study different disease or
outcomes.
Disadvantages:
• Only risk factors defined at the
beginning of the study can be
studied.
• Costly.
• Time consuming.
• For common diseases.
• The exposure status may
change during the study.
• Loss of follow up.

19. ANALYTIC STUDIES
Case Control Study:
Definition
It is analytic type of epidemiologic research design in which
the study population consists of groups who either have
(cases) or do not have (controls) a particular health problem
or outcome.

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Case Control Study:

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Case Control Study:
The investigator selects the case and the control group on
the bases of the outcome and compares them in term of their
frequency of past exposure to the possible exposure.

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Case Control Study:
Retrospective Study

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Case Control Study:
Cases
Controls

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Case Control Study:
Cases
Study subjects who have
outcome to be
investigated.
Case definition:
Objective description of the
case.
Eligibility Criteria.
Controls
Study subjects who do
not have the outcome to
be investigated.
Similar to the cases in
most of the aspects
except outcome.
Sources:
Hospital
Community

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Case Control Study:

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Case Control Study:
Controls
Cases
Similarity

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Case Control Study:
• Selection of controls:
– No outcome.
– Selection randomly or Systematic.
– Matching on specific variables./individual or
frequency.
– Restriction.

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Case Control Study:
What is the Potential Source of Study
Subjects…… ?

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Case Control Study:
The most important bias is recall .

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Case Control Study:
•
•
•
•
•
•
Advantages:
Quick design saves time.
Easy to perform.
Inexpensive.
Suitable for rare diseases.
Can study many risk factors.
Useful for generating
hypothesis.
Disadvantages
•
•
•
•
Recall bias.
Can not be used for incidence rate.
Temporal relationship.
Can study only one disease
outcome.
• Can only obtain relative measure
of risk.

32. Practical Exercise