Study Designs in reasearch
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Transcript of Study Designs in reasearch
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Study DesignsStudy DesignsAA
PresentationPresentation
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Types of Study designsTypes of Study designs
Non Intervention StudiesNon Intervention StudiesDescriptive studiesDescriptive studies
Comparative (analytical) studiesComparative (analytical) studies
Exploratory studiesExploratory studies
Intervention StudiesIntervention Studies
The two categories of intervention studiesThe two categories of intervention studies
are:are:
Experimental studiesExperimental studies
Quasi-experimental studies.Quasi-experimental studies.
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E P I D E M I O L O G I C A L S
1 . C a s e
2 . C a s e
3 . C o r r e l a t
4 . C r o s s S e
D E S C R I
C O H
C A S E
O B S E R V
3 . T r i
2 . D o u
1 . S i n
E X P E R I M
A N A L Y T
CurrentCurrent
ClassificationClassification
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Descriptive StudiesDescriptive Studies
Descriptive studies involve theDescriptive studies involve the
systematic collection andsystematic collection and
presentation of data to give apresentation of data to give a
clear picture of a particularclear picture of a particular
situation and can be carried outsituation and can be carried out
on a small or large scale.on a small or large scale.
Case studiesCase studies
Case seriesCase series
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Comparative or AnalyticalComparative or Analytical
StudiesStudies
An ANALYTICAL STUDY attempts toAn ANALYTICAL STUDY attempts toestablish causes or risk factors forestablish causes or risk factors for
certain problems. This is done bycertain problems. This is done by
comparing two or more groups,comparing two or more groups,
some of which have or develop thesome of which have or develop the
problem and some of which haveproblem and some of which have
notnot..
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Quantify the distribution of certain variables in aQuantify the distribution of certain variables in astudy population at a point of time. They maystudy population at a point of time. They may
cover, for example:cover, for example:
Physical characteristics of people, materials, or thePhysical characteristics of people, materials, or theenvironment,etcenvironment,etc
The behavior of people and the knowledge, attitudes,The behavior of people and the knowledge, attitudes,beliefs, and opinions that may help to explain thatbeliefs, and opinions that may help to explain that
behaviour (KAP studies), or events that occurred inbehaviour (KAP studies), or events that occurred in
the population.the population.
Cross-sectional surveys cover a sample of theCross-sectional surveys cover a sample of thepopulation. If a cross-sectional study covers the totalpopulation. If a cross-sectional study covers the totalpopulation it is called a census.population it is called a census.
Cross SectionalSurveys
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Case Control StudiesCase Control Studies
In a CASE-CONTROL STUDY, theIn a CASE-CONTROL STUDY, theinvestigator compares one groupinvestigator compares one group
among whom a problem is (e.g.,among whom a problem is (e.g.,
malnutrition) with anothermalnutrition) with another
group, called a control orgroup, called a control or
comparison group, where thecomparison group, where the
problem is absent to find outproblem is absent to find outwhat factors have contributed towhat factors have contributed to
the problem.the problem.
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Cohort StudiesCohort Studies
In a COHORT STUDY, a group of individuals thatIn a COHORT STUDY, a group of individuals thatis exposed to a risk factor (study group) isis exposed to a risk factor (study group) is
compared with a group of individuals notcompared with a group of individuals not
exposed to the risk factor (control group).exposed to the risk factor (control group).
The researcher follows both groups over time andThe researcher follows both groups over time andcompares the occurrence of the problem that he or shecompares the occurrence of the problem that he or she
expects to be related to the risk factor in the two groupsexpects to be related to the risk factor in the two groups
to determine whether a greater proportion of those withto determine whether a greater proportion of those with
the risk factor are indeed affected.the risk factor are indeed affected.
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Relative Ratio (RR)Relative Ratio (RR)
Ratio of incidence of the disease (orRatio of incidence of the disease (ordeath)among exposed and thedeath)among exposed and the
incidence among non-exposed.incidence among non-exposed.
It is a direct measure (or index) ofIt is a direct measure (or index) of
the strength of the associationthe strength of the association
between suspected cause and effectbetween suspected cause and effect
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Exploratory StudiesExploratory Studies
An Exploratory study is a small-scaleAn Exploratory study is a small-scale
study of relatively short duration,study of relatively short duration,
which is carried out when little elsewhich is carried out when little elseis known about a situation or ais known about a situation or a
problem.problem.
I i
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InterventionIntervention
StudiesStudies
In intervention studies, the researcherIn intervention studies, the researchermanipulates a situation and measuresmanipulates a situation and measures
the effects of the manipulation. Usuallythe effects of the manipulation. Usually
(but not always) two groups are(but not always) two groups are
compared, one in which the interventioncompared, one in which the intervention
takes place (e.g.. treatment with atakes place (e.g.. treatment with a
certain drug) and another group thatcertain drug) and another group that
remains "untouched" (e.g., treatmentremains "untouched" (e.g., treatment
with a placebo) .with a placebo) .
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Experimental StudiesExperimental Studies
Experimental design is the only type ofExperimental design is the only type ofstudy design that can actually provestudy design that can actually prove
causation.causation.
In an EXPERIMENTAL STUDY, individuals areIn an EXPERIMENTAL STUDY, individuals are
randomly allocated to at least two groups.randomly allocated to at least two groups.
One group is subjected to an intervention orOne group is subjected to an intervention or
experiment, while the other group(s) is not.experiment, while the other group(s) is not.
The outcome of the intervention - effect of theThe outcome of the intervention - effect of theintervention on the dependentintervention on the dependent
(variable/problem) is obtained by(variable/problem) is obtained by
comparing the two groups.comparing the two groups.
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The classical experimental studyThe classical experimental study
design has threedesign has three
characteristics:characteristics:
ManipulationManipulation
ControlControlRandomizationRandomization
Classical ExperimentalStudy Design
Q i i lQ i E i t l
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Quasi ExperimentalQuasi Experimental
StudiesStudies
In a QUASI-EXPERIMENTAL STUDY,In a QUASI-EXPERIMENTAL STUDY,at least one characteristic of a trueat least one characteristic of a true
experiment is missing.experiment is missing.
One of the most common quasi-One of the most common quasi-experimental designs uses two (or more)experimental designs uses two (or more)
groups, one of, which serves a controlgroups, one of, which serves a control
group in which no intervention takesgroup in which no intervention takes
place.place.
Both groups are observed before as wellBoth groups are observed before as wellas after the intervention, to test if theas after the intervention, to test if the
intervention has made any difference.intervention has made any difference.