Study design, Epidemiological study designA 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.

1. STUDY DESIGNS
- An Overview
Dr Lipilekha Patnaik
professor, Community Medicine
Institute of Medical Sciences & SUM Hospital,
Siksha ‘O’ Anusandhan deemed to be University
Bhubaneswar, ODISHA, INDIA
E mail– drlipilekha@yahoo.co.in
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2. Session Outline
Study designs and its types
Observational and Interventional studies
Uses of different studies
Systematic review and metaanalysis
Hierarchy of study designs in research
An introduction to Qualitative study
Ideal study design for different situations
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3. 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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4. TYPES
QUANTITATIVE QUALITATIVE
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5. Quantitative vs Qualitative
vQuantitative research is used to quantify the
problem by way of generating numerical data
which can be transformed into useable
statistics. It can generalize results from sample
to population.
vQualitative research is exploratory research.
It is used to gain an understanding of
underlying reasons, opinions etc. and provides
insight into the problem.
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7. Types of epidemiological studies
Types of studies Alternative name Unit of study
OBSERVATIONALSTUDIES
◦ Descriptive studies – Case report, case series Individuals
◦ Cross sectional surveys
◦ Analytical studies
◦ Ecological Correlation Populations
◦ Cross-sectional Prevalence Individuals
◦ Case-control Case-reference Individuals
◦ Cohort Follow-up Individuals
EXPERIMENTALSTUDIES (Intervention Studies)
◦ Randomized control trials Clinical Trials Patients
◦ Field trials Healthy People
◦ Community trial Community studies Communities
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8. DESCRIPTIVE STUDIES
ØDescriptive study is the first phase of epidemiological
investigation.
ØObserving the distribution of disease or health related
events in human population.
ØIdentify the characteristics with which the disease is
associated.
ØBasically 3 questions are asked when, where and who
i.e. Time, place and person distribution.
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9. Case reports
Case series
Population studies
(Cross sectional surveys)
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10. Case Reports
ØDetailed presentation of a single case.
ØGenerally report a new or unique finding
üe.g. previous undescribed disease
üe.g. unexpected link between diseases
üe.g. unexpected new therapeutic effect
üe.g. adverse events
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11. Case Series
ØExperience of a group of patients with a
similar diagnosis
ØCases may be identified from a single or
multiple sources
ØGenerally report on new/unique condition
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12. Cond.
ØAdvantages
•Useful for hypothesis generation
•Informative for very rare disease with few
established risk factors
ØDisadvantages
•Cannot study cause and effect relationships
•Cannot assess disease frequency
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13. Case Report
Case Series
One case of unusual
findings
Multiple cases of
findings
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15. Uses
Hypothesis generation
Suggesting associations
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16. ANALYTICAL STUDIES
Ecological study
Cross-sectional
Case-control
Cohort
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17. Ecological Study
žIt is not easy to establish links between environmentalexposures
and health outcomes using individuallevel data.
žEcological study designs provide one way of avoiding these
difficulties and studying the effects of environmentalexposures on
different health outcomes.
žEcological studies look for associations between the occurrenceof
disease and exposure to known or suspected causes.
žHowever, the unit of analysis is not an individualbut a population /
a group of persons
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19. Cross-sectional Study
Data collected at a single point in time
An “observational” design that surveys exposures and
disease status at a single point in time (a cross-section
of the population)
Describes associations
Prevalence
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A “Snapshot”

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time
Study only exists at this point in time
Study
population
No Disease
Disease
factor present
factor absent
factor present
factor absent

21. Sample of Population
Playing
outdoor games
regularly
Not playing
outdoor games
Prevalence of
Overweight/
obesity
Prevalence of
Overweight/
obesity
Time Frame = Present
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Defined Population of school
going adolescents
Example

22. Why we do cross-sectional study?
ØTo assess the burden of disease in a population
and to assess the need for health services.
ØTo compare the prevalence of disease in
different populations.
ØTo examine trends in disease prevalence or
severity over time.
ØTo find out association
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25. Case-Control Studies
§Start with people who have disease (Cases)
§Match them with controls that do not have
disease
§Look back and assess exposures
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26. Other Name Retrospective Study
Unit of Study Cases/Control
Study QuestionWhat has happened ?
Direction of Inquiry= F O
Study Design
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Study
population
Cases
(disease)
Controls
(no disease)
factor present
factor absent
factor present
factor absent
present
past
time
Study begins here

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Obese adolescents
Normal adolescents
PresentPast
No Outdoor games
No Outdoor games
Regular outdoor games
Regular outdoor games
Cases
Controls
Example

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30. Cohort Study
Cohort is defined a group of people who share a
common characteristic or experience within a
defined time period (age, occupation, exposure)
Birth cohort, exposure cohort
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31. Begin with disease-free individuals
Classify patients as exposed/unexposed
Record outcomes in both groups
Compare outcomes using relative risk
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32. Other Name Prospective Study / Follow-up
Study/Incidence Study
Unit of Study Individual
Study Question What is happening ?
Directionof Inquiry F O
Study Design
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time
Study begins here
Study
population
free of
disease
Factor
present
Factor
absent
disease
no disease
disease
no disease
present future

34. Example
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Not playing
outdoor games
Playing outdoor
games regularly
Not obese
Obesity
Obesity
Not obese
Present Future
Cohort of
School going
adolescents

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36. EXPERIMENTAL STUDIES
1. Experimental studies are similar in approach to cohort studies
excepting that the study condition are under direct control of the
investigator.
2. There is some action, intervention or manipulation which are
deliberate.
AIM OF EXPERIMENTAL STUDY
1. To provide scientific proof of aetiological factor.
2. To provide a method of measuring the effectiveness and efficiency of
health services for the prevention control and treatment of diseases.
TYPES OF EXPERIMENTAL STUDIES
1. Animal study
2. Human study
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37. Types
1. Randomised controlled trials
2. Non-randomised trials.
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38. 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 (Intervention with Standard of care or placebo)
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39. Experimental Design
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time
Study begins here (baseline point)
Study
population
Intervention
Control
outcome
no outcome
outcome
no outcome
baseline
future
RANDOMIZATION

40. Participants are allocated in to two groups.
1) study group : To receive preventive and
therapeutic manoeuvres.
2) control group : Not to receive any
intervention or to receive standard of care.
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Randomisation

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time
Study begins here
obese students
Intervention
(Regular exercise
&Outdoor games)
Control
Decrease BMI
No change of BMI
Decrease BMI
No change of BMI
Obese
students Future
(After 2 years)
RANDOMIZATION

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43. Different studies have different uses
Objective Type of study
Prevalence Cross-sectional
Incidence Cohort
Causal association Cohort
Case-control
Prognosis Cohort
Natural history of
disease
Cohort
Treatment effect Randomised Controlled
Trial
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44. Did the investigator assign
exposure?
Experimental Study Observational Study
Yes No
Random Allocation?
Comparison Group?
Yes Yes
No
No
Analytical
Study
Descriptive
Study
Randomized
Control
trial
Non-
Randomized
Control trial
Direction?
Exposure Outcome
Exposure and
outcome at
the same time
Cohort
Study
Case
Control
Study
Cross-
Sectional
Study
Exposure Outcome
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45. Systematic Review
“A review that is conducted according to clearly stated, scientific
research methods, and is designed to minimize biases and errors
inherent to traditional, narrative reviews.”
Margaliot, Zvi, Kevin C. Chung. Systematic Reviews: A Primer for Plastic Surgery Research. PRS Journal.
120/7 (2007)
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46. Meta analysis
ØMeta-analysis is a statistical analysis of a collection of
studies.
ØMeta-analysis methods focus on contrasting and comparing
results from different studies in anticipation of identifying
consistent patterns and sources of disagreements among
these results.
Ø“While all meta-analyses are based on systematic review of
literature, not all systematic reviews necessarily include meta-
analysis.”
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47. Hierarchy of Study Design
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48. QUALITATIVE RESEARCH
Qualitative research can provide insight into
the priblem which is not possible with purely
quantitative data
• A means for exploring and understanding the
meaning individuals or groups ascribe to social or
human problems
• Study human behavior and social world
Help us to understand the world in which we
live and why things are the way they are
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49. Qualitative research answer questions on:
◦Why people behave the way they do
◦How opinions and attitudes are formed
◦How people are affected by the events that
go on around them
◦How and why cultures have developed
◦The difference between social groups
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50. Which is the ideal study design?
§A rare case of Dermatomyositis came to the hospital –
Case report
§Prevalence of Hypertension among adolescents in Bhubaneswar city –
Cross sectional
§To find out the association of bottle feeding with the incidence of diarrhea –
Cohort
§Association of Smoking and MI –
Case Control
§Safety and efficacy of Malaria vaccine –
RCT
§To explore factors of nonuse of contraceptives in a tribal community –
Qualitative study
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