This document discusses the analytical concepts and methodologies of case-control studies in epidemiology. Key topics include the definition and design of case-control studies, the steps involved in conducting them, their advantages and disadvantages, and their impact on public health. Emphasis is placed on the selection of cases and controls, the measurement of exposure, and the analysis of data to inform public health strategies.

1. Epidemiology
Unit vii (Epidemiological methods).
Presentation topic; (discuss the analytical
and basic concepts of case control)
Presented to; Madam Musarat Fatima
Date /14/02/2024
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2. GROUP MEMBERS
ARSALAN RAJPAR
ROOHULLAH
NAVEED ALI
PAWAN KUMAR
MUHAMMAD FAISAL
ASMA MUSTAFA
SHAILA
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3. OBJECTIVES
 At the end of presentation, students will be able to;
 Define case control study
 Define case control study design.
 Define the steps of case control study.
 Advantages and disadvantages of case control.
 Define odds ratio and how it is calculated.
 Discuss impact of case control studies on public health.
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6. Case control study
 Definition; A study that compares two groups
of people, those with the disease or condition
under study (cases) and a very similar group of
people who do not have the disease or
condition (controls).
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8. Steps of case control study
(1) Selection of cases and controls
(2) Matching
(3) Measurement of exposure
(4) Analysis and interpretation
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9. (1) Selection of cases and controls
 Selection of cases;
(a) Diagnostic criteria; clearly define the diagnostic
criteria for the disease being studied, including any
specific stages(e.g. breast caner stage 1)
 The diagnostic criteria should be established before
the study begins and should remain unchanged
throughout the study.
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10. (1) Eligibility criteria; including only newly diagnosed
(incident) cases within a specific time period. This
helps ensure that cases are not old or in advanced
stages of the disease (prevalent cases) and to focus
on recent occurrences.
(b) Sources of cases
(1) hospitals; cases can be selected from hospitals,
either from a single hospital or a network of hospitals,
admitted within a specified period.
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11. (2) General population; in a population based control
study, identify all cases of the study disease within a
defined geographic area during a specified time period.
 Selection of controls;
The proper way to select controls in a case
control study involves these key consideration
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12. (a) Selection criteria;
(1) Hospital controls;
they can be chosen from same hospital
as the cases but with different illnesses than the
disease under study. For instance, if studying
cervical cancer patients, the control group might
consist of patients with breast cancer, digestive
tract cancer or other non related conditions
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13. (2) Relatives; The control may also be taken up from
relatives (spouses and siblings). Siblings control are
unsuitable where genetic conditions are under study.
(3) Neighborhood controls; The controls may be
drawn from persons living in the same locality as cases,
persons working in the same factory or children
attending the same school.
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14. (4) General populations;
population controls can be
obtained from defined geographic areas, by
taking a random sample of individuals free of
the study disease.
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15. (2) Matching
Matching involves selecting controls who are
similar to cases in certain characteristics such as
age, gender or other relevant factors. This helps
to reduce potential confounding variables and
increases the validity of the study
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16. Continue….
Matching can be done in different ways, such as
individual matching or frequency matching. It is
an important step to ensure a more accurate
comparison between cases and controls.
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17. (3) Measurement of exposure
When it comes to measuring exposure,
researchers use different methods depending on
the specific risk factor they are studying.
For example, if they are investigating the effect
of smoking on a disease, they might use self
reporting or questionnaires to gather
information on smoking habits.
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18. Continue…
 The goal is to gather accurate and reliable data
to understand the relationship between the
exposure and the disease outcome.
Measurement of exposure is a critical step in
epidemiological research to ensure valid and
meaningful results.
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19. (4) Analysis
The final step is analysis, to find out
(a) Exposure rates among cases and controls to
suspected factor
(b) Estimation of disease risk associated with
exposure (odds ratio)
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20. (a)Exposure rates
A case control study provides a direct
estimation of the exposures rates
(frequency of exposure) to a suspected
factor in disease and non disease groups
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21. (b)Relative of risk
 It is defined as , the ratio between the incidence of
disease among exposed persons and incidence
among non exposed it is given by formula;
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22. Odds ratio
 An odds ratio is a measure of association
between a certain events ‘’a’’ and a second
event ‘’b’’. Larger the odds ratio, the more
likely the event is to be found with exposure
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24. Interpretation 24

25. Advantages
 Relatively easy to carry out
 Rapid and inexpensive
 Require comparatively few subjects.
 Particularly suitable to investigate rare disease
or disease about which is little known. But a
disease which is rare in general population(e.g.
leukemia in adolescents) may not be rare in
special exposure group.
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 Allows the study of several different etiological
factors (e.g. smoking and physical inactivity in
myocardial infarction.
 Risk factors can be identified.
 No attrition problems, because case control
studies do not follow up of individuals into the
future.
 Ethical problems minimal.
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27. Disadvantages
 Selection of an appropriate control group may
be difficult.
 Do not distinguish between causes and
associated factors.
 Not suited to the evaluation of therapy or
prophylaxis of disease.
 Another major concern is the representative of
cases and controls.
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28. Continue….
 Difficulty in determining causality
 Limited ability to study multiple outcomes or
exposures
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29. Impact of case control study on public
health
 Case control studies have a significant impact
on public health. They play a crucial role in
identifying risk factors and potential causes of
disease. By examining the association between
exposures and outcomes.
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30. Continue…
 Case control studies provide valuable
information for developing preventive
strategies and interventions. This knowledge
helps public health professionals make
evidence based decisions, implement targeted
interventions and allocate resources effectively.
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31. Continue…
 Case control studies contribute to our
understanding of disease etiology, guide
public health policies, and ultimately help to
improve the overall health and well being of
communities.
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32. References
 K- park’s preventive and social medicine
 My AI snapchat
 www.google.com.pk
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