Daw Khin Saw Naing
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oNon-intervention studies in which
the researcher just observes and
analyses researchable objects or
situations but does not intervene
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 Intervention studies
in which the
researcher
manipulates objects
or situations and
measures the
outcome of his
manipulations
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oNon-intervention studies in which
the researcher just observes and
analyses researchable objects or
situations but does not intervene
Exploratory studies
Descriptive studies
Comparative (analytical)
studies
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Large scale
cross-sectional surveys
Cross-sectional surveys aim at
describing and quantifying the
distribution of certain variables in a
study population
at one point of time.
Small scale, descriptive case studies
Descriptive case studies describe indepth the characteristics of one or a
limited number of "cases".
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Large scale
cross-sectional surveys
The behaviour or practices
of people and the
knowledge, attitudes,
beliefs, opinions which
may help to explain that
behaviour (KAP studies), or
Events that occurred in
the population
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Comparative or
Analytical Studies
This is done by
comparing two or
more groups,
some of which have or
develop the problem
and
some of which have
not
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Comparative or
Analytical Studies
An ANALYTICAL STUDY
attempts to establish
causes or risk factors
for certain problems.
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In a CASE-CONTROL
STUDY
the investigator compares
TWO GROUPS
and in order to find out
what factors have
contributed to the
problem..
another group called a
control or comparison
group, where the problem
is absent,
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one group among
whom the problem
that he wishes to
investigate is
present
(e.g. malnutrition)
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• The investigator looks back in
time to measure exposure of
the study subjects.
• The exposure is then compared
among cases and controls to
determine if the exposure could
account for the health condition
of the cases
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Characteristics
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EXPOSURE
DISEASE
COHORT
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EXPOSURE
DISEASE
CASE CONTROL
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CASES
d/s +
EXPOSED
CONTROL TOTAL
d/s -
++
+-
-+
--
Exposure +
NON
EXPOSED
Exposure -
TOTAL
ODDS RATIO = (++) (--) / (+-) (-+)
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Ca Lung CONTROL TOTAL
d/s +
d/s SMOKER
60
20
40
180
100
200
Exposure +
NON
SMOKER
Exposure -
TOTAL
ODDS RATIO = (++) (--) / (+-) (-+)
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Why case-control design for study of rare
diseases?
Case-Control Studies for
Diseases having long induction/ latent
period
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Progression of study design:
 Clinical research
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 Community research
Non-interventions studies
Case-Control Studies
Controls
should come from
the same “source” population.
For example, in a hospital case-control study where
cases are being sought in the hospital, cases should
normally be selected from patients attending at the
same hospital.
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Non-interventions studies
Case-Control Studies
Matching
means taking care that the cases and
controls are similar with respect to
the distribution
of one or more potentially
confounding variables.
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Non-interventions studies
Case-Control Studies
Matching
However,
we cannot then look at the effect
of the matched variable as a risk
factor because we have made
the cases and controls exactly
the same with respect to that
variable.
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CASE CONTROL Studies
 ADVANTAGES
 The most efficient design :
 TIME
 MONEY
 EFFORT
 Appropriate for diseases with low
incidence
 Appropriate for conditions with Long
latent period
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CASE CONTROL Studies
 DISADVANTAGES
 Problems in choosing a control group: deciding who should be
the controls….matched or unmatched..
 Not appropriate for conditions in which the frequency of
exposure is low
 Recall Bias: difficult to ascertain exposure history
 Can not calculate Incidence
 Can not calculate risk: RR AR ARR
 Can get only the closet estimate of Relative Risk
….ODDS RATIO
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