This document discusses different study designs used in research. It defines a study design as a specific plan for conducting a study that allows the investigator to translate a conceptual hypothesis into an operational one. The document outlines different types of study designs including descriptive studies, analytical observational studies like cross-sectional studies, case-control studies, and cohort studies, as well as experimental/interventional studies. For each study design, it provides details on the unit of study, study question, direction of inquiry, and key aspects of the design.
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Study design in research
1. STUDY DESIGN
IN
RESEARCH
* Few jewels from ocean
Dr. Kusum Gaur
Professor, PSM
WHO Fellow IEC
3. Steps in Research (Holy 11)
1. Collect review of literature/Situation Analysis
2. Identify and prioritize health problems
3. Decide aims & objectives
4. Planning Methodology including study design
5. Execution
6. Compilation, Classification & Presentation of data
7. Analysis
8. Test of Significance/Test of Hypothesis
9. Inferences
10. Report Writing
11. Dissemination of Report
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4. Study Design
A study design is a specific plan or protocol
for conducting the study,
which allows the investigator
to translate the conceptual hypothesis
into an operational one.
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5. Direction of Study
Backward Forward
Cross -sectional
Retrospective Prospective
3
4. Ambidirectional
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6. Decision Tree
Intervention Done
No Yes
Observational Study Experimental Study
Comparison Group Randomization
No Yes
No Yes
Descriptive Study Analytic Study
NRCT Study RCT Study
Direction of Study
E O E O
Cohort Study E = O Case-Control Study
Cross-Sectional Study
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7. Epidemiological Study Design
Observational Studies
Descriptive Studies
Analytic
Cross-Sectional
Case-Control
Cohort
Experimental / Interventional studies
As per Control: RCT/NRCT
As per Blinding: Single /Double Blind
As per Design: Simple/Cross-over
As per Area: Field/Clinical/Lab
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8. Descriptive Studies
• Case reports
• Case series
• Population studies
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9. Descriptive Studies: Uses
• Hypothesis generating
• Suggesting associations
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10. Descriptive Type of Observational Study
• Other Name Case-Series/Population
• Unit of Study Case/Individuals
• Study Question What is happening
• Direction Of Inquiry
• Study Design
☻☻☻☻☻☻ desired information
☻☻☻☻☻☻ about cases/individuals is collected
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11. Case-Series …….
Advantages
• Easy to do
• Excellent at identifying unusual situation
• Good for generating hypotheses
Disadvantages
• Generally short-term
• Investigators self-select (bias!)
• no controls
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13. Cross-sectional Study
• Data collected at a single point in time
• Describes associations
• Prevalence
A “Snapshot”
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14. Cross-Sectional Study
• Other Name Prevalence Study
• Unit of Study Individual
• Study Question What is happening
• Direction of Inquiry
• Study Design Exposed
to Factor
Not
Exposed
Diseased to Factor
Population Exposed to
Factor
Non-
Disease Not
Exposed to
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15. Objectives of a Cross-Sectional Study
To find out association
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16. Cross-sectional Study
Sample of Population
Defined Population
Regular Not doing meditation
Meditation
Prevalence of Prevalence of
DM DM
Time Frame = Present
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17. Cross-sectional Study
E.G. Out of 1000 population if 100 were doing meditation regularly &
out of that only 2 were having DM. Remaining 900 were not doing
meditation at all, out of that 220 were having DM.
+ DM -
2 98
Meditation
+
- 220 680
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18. Cross-Sectional Study
• Strengths
– Quick
– Cheap
• Weaknesses
– Cannot establish cause-effect
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19. Case-Control Studies
Start with people who have disease(Cases)
Match them with controls that do not have
disease (Match Confounding)
Look back and assess exposures
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20. Controls
A control is a standard of comparison
(confounded with variability but without
effect)
for
• Effects
• Variability
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21. Case-Control Study
• Other Name Retrospective Study
• Unit of Study Cases/Control
• Study Question What has happened
• Direction of Inquiry= F O
• Study Design
Exposed
Cases
Not
Exposed
Exposed
Control
Not
Exposed
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22. Objective of a Case-Control Study
To find out association
To assess Risk Ratio
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23. Case-Control Study
Cases
Regular Meditation
Patients with DM
No Meditation
Controls
Regular Meditation
Persons w/o DM
No Meditation
Past Present
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24. The logic of Case-Control Studies
Cases differ from controls only in having the
disease
If exposure does not predispose to having the
disease, then exposure should be equally
distributed between the cases and controls.
The extent of greater previous exposure among
the cases reflects the increased risk that
exposure confers
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25. Case-Control Studies: Strengths
• Good for rare outcomes: cancer
• Can examine relation of exposures to disease
• Useful to generate hypothesis
• Fast
• Cheap
• Provides Odds Ratio
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26. Case-Control Studies: Weaknesses
• Cannot measure
– Incidence
– Prevalence
– Relative Risk
• Can only study one outcome
• High susceptibility to bias
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27. Cohort Study
• Begin with disease-free individuals
• Classify patients as exposed/unexposed
• Record outcomes in both groups
• Compare outcomes using relative risk
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28. Cohort Study
• Other Name Prospective Study / Follow-up Study/Incidence Study
• Unit of Study Individual
• Study Question What is happening
• Direction of InquiryF O
Diseased
• Study Design
• Exposed to
Factor
Not Non
Diseased
Cohort
Cohort Diseased
Not
Exposed to
Factor
Non-Diseased
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29. Logic of Cohort Study
Cohort is a group of persons sharing a
common characteristics
Differences in the rate at which exposed and
control subjects contract a disease is due to
the differences in exposure, since others are
known and similar.
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30. Cohort Study
Prospective (usually)
Controlled
Can determine causes and incidence of
diseases as well as identify risk factors
Generally expensive, time consuming and difficult
to carry out
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31. Steps for Cohort Study
Identify geographically defined group
Identify exposed subjects and not exposed
subjects
Follow over a specific time
Record the fraction in each group who
develop the condition of interest
Compare these fractions using RR, AR or OR
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32. Objectives of a Cohort Study
To find out association
To assess Risk Ratio
To find out Relative Risk
To find out Attributed Risk
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33. Prospective Cohort Study
DM
No Meditation
No DM
Cohort
DM
Regular
Meditation No DM
Present Future
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34. Cohort Study: Strengths
• Can measure multiple outcomes
• Can adjust for confounding variables
• Can calculate Attributed Risk
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35. Cohort Study: Weaknesses
• Expensive
• Time consuming
• Cannot study rare outcomes
• Confounding variables
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36. Measurements of Association
Cohort Study Case Control Study
•Significance Test •Significance Test
•Relative Risk •OR
•Attributable Risk
•OR
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37. Measures of Association
Significance Test – to test significance of difference
in exposure between control and Cases
Odds ratio - ratio of the odds of contracting
disease in given exposure
Relative Risk – Ratio between incidence among
exposed and incidence among non-exposed
Attributed Risk – percentage of difference between
incidence among exposed and non-exposed with
incidence among exposed
RR or OR of 1 indicate no effect of exposure (equal odds)
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38. ‘Z’ Score of Exposure Rates
Cases control
Exposed a b
a x 1oo
Exposure Rates = in Cases Non- c d
exposed
(P2) a+c
b x 1oo
Exposure Rates = in Controls P2 – P1
(P1) b+d Z Score =
SEDP
P1 Q 1 P 2 Q 2
SEDP = ------------- + --------
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N1 N2
39. ad
ODD’s Ratio = Times
bc
Incidence among Exposed
RR = Times
Incidence among Non-Exposed
a/a+b a (c+d)
= =
c/c+d c (a+b)
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40. Attributed Risk
(Incidence among Exposed - Incidence among Non-Exposed)
AR = x 100
Incidence among Exposed
a
Incidence among Exposed= x 100
a+b
c
Incidence among Non-Exposed= x 100
c+d
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41. Experimental Studies
Clinical trials provide the “gold standard” of
determining the relationship between
factor and the event
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42. Types of Experimental Study
As per Randomization:
• Randomized Control Trials (RCT)
• Concurrent Parallel Design (RCT)
• Sequential RCT Design
• RCT with External Control
• Non – Randomized Trials
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43. Types of Experimental Study….
As per Construction:
• Simple
• Cross-Over Study Design
As per Study Area:
• Field Trials
• Clinical Trials
• Lab. Trials
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44. Quality of Experimental Study
• Randomization
• Blinding
• Control
• Cross-Over
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45. Controls in Clinical Trials
A clinical trial is a comparative, prospective
experiment conducted in human subjects
• Historical controls are better than no controls
• Patients can serve as own controls - This is
usually beneficial as the comparison removes
patient differences
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46. Blinding
Good practice: factors that can affect the
evaluation of outcome should not be permitted
to influence the evaluation process
Single-blind
Patient or evaluator (either of one) is blinded as
to intervention
Double-blind design
Neither patient nor outcome evaluator knows
Rx to which patient was assigned
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47. Randomized Control Trials
(RCT)
• Before and After Comparison
• Comparison with Placebo
• Comparison Of two medicine/procedure/tests
• Comparison Of > two medicine/procedure/tests
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48. Experimental Study
• Other Name Intervention Study
• Objective To know the effect of intervention
• Unit of Study Individual meeting entry criteria
• Study Question What is happening after intervention in both
groups
• Direction of Inquiry I E
• Study Design 1(Intervention with Placebo) Positive
Outcome
Group 1/cases Intervention
Negative
Outcome
Positive
Outcome
Group
Placebo
2/control
Negative
Outcome
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49. Clinical Trial
R Treatment
a Outcomes
Group
n
d
Study o
Population m
i
z Outcomes
e Control Group
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50. Intervention Study - Design 2
(Comparison of Effect of Two Interventions)
Cases
Meeting
Entry criteria
Group - 1 Group -2
Intervention -1 Intervention Intervention - 2
Positive Negative Positive
Outcome Negative
Outcome Outcome Outcome
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51. Cross Over Design
Group -1 Cases Group-2
Meeting
Entry
criteria Intervention - 2
Intervention - 1
Positive Negative
Positive Negative Outcome
Outcome Outcome
Outcome
Group -1
Group -2 Crossover
Intervention -2
Intervention -1
Positive Negative
Positive Negative
Outcome
Outcome Outcome
Outcome
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52. Other Types of Experimental Study
• Quincy Experimental Study
• Block Experimental Study
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53. Quincy Experimental Study
Cases
Meeting
Entry criteria
Group - 1 Group -2
Intervention Intervention No Intervention
Positive Negative Positive
Outcome Negative
Outcome Outcome Outcome
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54. Block Experimental Study
Cases
Meeting
Entry criteria
Group -3
Group - 1
Group -2
Intervention Intervention-3
Intervention -1 Intervention
Intervention-2
Positive Positive Negative
Negative
Outcome Outcome Outcome Outcome
Positive Negative
Outcome Outcome
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55. Steps of Experimental Study
Drawing up a Protocol
Reference Population
Sample Population
Exclusions
Randomization
Experimental Group Control Group
Manipulation/Intervention
Follow - up
12/08/2012 Assessment of Outcome
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57. STUDY QUESTIONS AND APPROPRIATE DESIGNS
Type of Question Appropriate Study Design
Burden of illness Field Surveys
- Prevalence Cross Sectional Survey
- Incidence Longitudinal survey
Causation, Risk & Prognosis Case Control Study,
Cohort study, RCT
Treatment Efficacy Randomized Controlled study
Diagnostic Test Evaluation Randomized Controlled study
Cost Effectiveness Randomized Controlled study
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58. Hierarchy of Epidemiological Study Design
Establish Causality RCT
Cohort
Case Control
Cross-Sectional
Case Series
Generate Hypothesis Case Report
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