This document provides an overview of different study designs used in epidemiological research, including observational studies like case reports, case series, cross-sectional studies, case-control studies, cohort studies, and experimental studies like randomized controlled trials. It discusses the advantages and disadvantages of each design and how they are used to study disease etiology, risk factors, and effects of interventions. Key points covered include how observational studies do not involve manipulation of exposures but can establish associations, while experimental studies allow investigation of cause-and-effect through controlled manipulation of exposures.

1. BY DINESH
M PHARM PHARMACOLOGY
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2. CONTENTS
 INTRODUCTION
 TYPES AND DESIGN
 EXPERIMENTAL STUDY
 OBSERVATIONAL STUDY
 REFERENCES
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3. INTRODUCTION
 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. CONT…
 Observational: Studies that do not involve any
intervention or experiment.
 Experimental: Studies that entail manipulation of the
study factor (exposure) and randomization of subjects
to treatment (exposure) groups.
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7.  Non-experimental.
 Observational because there is no individual
intervention.
 Treatment and exposures occur in a “non-controlled”
environment.
 Individuals can be observed prospectively,
retrospectively or currently.
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9. CASE REPORTS
 Detailed presentation of a single case or handful of
cases
 Generally report a new or unique finding
 e.g. previous undescribed disease
 e.g. unexpected link between diseases
 e.g. unexpected new therapeutic effect
 e.g. adverse events
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10. CASE SERIES
 Experience of a group of patients with a similar
diagnosis.
 Cases may be identified from a single or multiple
sources.
 Generally report on new/unique condition .
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11.  Advantages
Useful for hypothesis generation
Informative for very rare disease with few
established risk factors
 Disadvantages
Cannot study cause and effect relationships
Cannot assess disease frequency
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13. ANALYTICAL STUDY
 Group data
Ecologic study
 Individual data
Cross-sectional study
Case-control study
Cohort study
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14. ECOLOGICAL STUDY
 An investigation of the distribution of health and its
determinants between groups of individuals.
 Unit of study is the aggregate data not individual
level.
 It is usually be conducted as the first step study for
research.
 The result is difficult to interpret because of
confounding and bias.
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15.  Advantages
Cheap, quick and convenient since it usually
come from existing data.
 Disadvantages
Inability to link exposure with disease in
individual (ecological fallacy)
Limit to control effect of other factors
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16. CROSS SECTIONAL STUDY
 An “observational” design that surveys exposures and
disease status at a single point of time (a cross-section
of the population)
 ADVANTAGES
Gives general description or scope of
problem.
Useful in health service evaluation and
planning.
Baseline for prospective study .
Low-cost.
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17.  DISADVANTAGES
No calculation of risk.
Temporal sequence is unclear.
Not good for rare diseases.
Selective recall can lead to bias
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18. CASE CONTROL STUDY
 An “observational” design comparing exposures in
disease cases vs. healthy controls from same
population.
 Exposure data collected retrospectively.
 Most feasible design where disease outcomes are rare.
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19. ODDS RATIO
Odds ratio= ad/bc
ADVANTAGES
Cheap, easy and quick studies
Require comparatively few subjects
DISADVANTAGES
If the incidence of exposure is high, it is difficult to
show the difference between cases and controls
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SUSPECTED
RISK FACTOR
CASE CONTROL
PRESENT A B
ABSENT C D
A+C B+D

20. COHORT STUDY
 An “observational” design comparing individuals with
a known risk factor or exposure with others without
the risk factor or exposure.
 Looking for a difference in the risk (incidence) of a
disease over time.
 One of best observational design.
 Data usually collected prospectively (some
retrospective)
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22.  ADVANTAGES
Can establish population-based incidence.
Accurate relative risk (risk ratio) estimation.
Can be used where randomization is not possible.
 DISADVANTAGES
Lengthy and expensive.
May require large samples.
Not suitable for rare diseases.
Not suitable for diseases with longlatency
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24.  Treatment and exposures occur in a “controlled”
environment.
 Planned research designs.
 Clinical trials are the most well known experimental
design.
 Investigator can “control” the exposure akin to
laboratory experiments except living populations are the
subjects.
 Generally involves random assignment to groups.
 The ultimate step in testing causal hypotheses
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25. RANDOMIZED CONTROLLED TRIAL
 A design with subjects randomly assigned to
“treatment” and “comparison” groups.
 Provides most convincing evidence of relationship
between exposure and effect.
 Not possible to use RCTs to test effects of exposures
that are expected to be harmful for ethical reasons.
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26. The basic steps include the following:
• Drawing up ‘Protocol’
• Selection of Reference and Experimental Population.
• Randomization
• Manipulation or Intervention
• Follow-up
• Assessment of outcome
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29.  ADVANTAGES
Ability to randomize subjects.
Temporal sequence of cause and effect.
Can control extraneous variables.
Best evidence of causality
 DISADAVANTAGES
Expensive.
It may be unethical to assign persons to certain
treatment or comparison groups
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30.  Other Types of Experimental Study
Field trials
 Community trials
 Animal studies
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31. Non-Randomized Trials
 Also known as Quasi-Experimental Designs.
 It is a type of research in which the investigator manipulates the
study factor but does not assign individual subjects randomly to
the exposed & non- exposed groups.
 These are designed as:
• It is always not possible for ethical, administrative and
other reasons to resort to a RCT.
• Some preventive measures apply only to groups or
community-wide basis.
• When disease RCT require follow-up of thousands of
people for a decade or more.
• As here randomization is not done. So, low comparability than
RCT and chances of spurious results are high than RCT.
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32.  These studies may be of following types:
 Uncontrolled Trials
 Natural Experiments
Before and after comparison studies
• With control
• Without control
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33. META ANALYSIS
 Meta-analysis is a statistical analysis of a collection of
studies.
 Meta-analysis methods focus on contrasting and
comparing results from different studies in
anticipation of identifying consistent patterns and
sources of disagreements among these results.
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34. REFERENCES
 Epidemiology by Leon Gordis, 5th Edition
• Textbook of Public Health and Community Medicine by
Rajvir Bhalwar
• Park’s Textbook of Preventive and Social Medicine by K.
Park, 23rd Edition
• Jekel’s Epidemiology, Biostatistics, Preventive Medicine,
and Public Health by David L Katz et al, 4th Edition
• Health Research Methodology : A Guide for Training in
Research Methods, 2nd Edition
• Basic Epidemiology by R Bonita
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