The document discusses different study designs used in research, including observational studies like case reports, case series, cross-sectional studies, and cohort studies, as well as experimental studies like randomized controlled trials. It describes the key characteristics and advantages and disadvantages of each design. The highest level of evidence comes from randomized controlled trials, while observational studies are useful for initial hypothesis generation.
2. 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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4. CONTD.
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. OBSERVATIONAL STUDIES
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. CONTD.
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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14. BASIC QUESTION IN ANALYTIC STUDY
Are exposure and disease linked?
Exposure Disease
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15. ANALYTIC STUDY
Group data
Ecologic study
Individual data
Cross-sectional study
Case-control study
Cohort study
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16. ECOLOGICAL STUDY
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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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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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18. CROSS-SECTIONAL STUDIES
An “observational” design that surveys
exposures and disease status at a single
point of time (a cross-section of the
population)
time
Study only exists at this point in time
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19. CONTD.
time
Study only exists at this point in time
Study
population
No Disease
Disease
factor present
factor absent
factor present
factor absent
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20. CONTD.
Often used to study conditions that are
relatively frequent with long duration of
expression (nonfatal, chronic
conditions)
It measures prevalence, not incidence
of disease
Not suitable for studying rare or highly
fatal diseases or a disease with short
duration of expression
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21. 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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23. 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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25. ODDS RATIO
Odds ratio= ad/bc
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Suspected
Risk Factor
Cases Controls
Present a b
Absent c d
a+c b+d
26. ADVANTAGES
Cheap, easy and quick studies
Require comparatively few subjects
Multiple exposures can be examined
Rare diseases and diseases with long
latency can be studied
Suitable when randomization is unethical
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27. DISADVANTAGES
Case and control selection troublesome
Subject to bias
Direct estimation of incidence is not
possible
If the incidence of exposure is high, it is
difficult to show the difference between
cases and controls
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28. 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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31. ADVANTAGES
Can establish population-based incidence
Accurate relative risk (risk ratio)
estimation
Can be used where randomization is not
possible
Selection and information biases are
decreased
Multiple outcomes can be studied
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32. DISADVANTAGES
Lengthy and expensive
May require large samples
Not suitable for rare diseases
Not suitable for diseases with long-
latency
Unexpected environmental changes may
influence the association
Nonresponse, migration and loss-to-
follow-up biases
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34. EXPERIMENTAL STUDY
Treatment and exposures occur in a
“controlled” environment
Planned research designs
Clinical trials are the most well known
experimental design.
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35. CONTD.
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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36. 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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37. time
Study begins here (baseline point)
Study
population
Intervention
Control
outcome
no outcome
outcome
no outcome
baseline
future
RANDOMIZATION
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38. The “gold standard” of research
designs
Provides most convincing evidence of
relationship between exposure and
effect
Trials of hormone replacement
therapy in menopausal women
found no protection for heart
disease, contradicting findings of
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CONTD.
39. Ability to randomize subjects
Temporal sequence of cause and effect
Can control extraneous variables
Best evidence of causality
ADVANTAGES
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41. Other Types of Experimental Study
Field trials
Community trials
Animal studies
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42. 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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