1. Observational Study- An Overview
Dr. Satyabrata Sahoo
DM Clinical Pharmacology
Resident
Dept. of Clinical & Experimental
Pharmacology, CSTM, kolkata
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2. Introduction
• Observational study is a study where there is
no intervention.
• Observational studies are sometimes referred
as quasi-experimental or a natural
experiments1
• a well-planned or designed observational
study can produce a good result next to
Randomised controlled trial2
• Includes Cohort, Case-control, Cross-
sectional studies
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6. Cross –sectional studies
• It is a study design in which exposure and
outcome are determined simultaneously for
each subject
• Widely used to understand the prevalence of
various conditions, treatments, services or other
outcomes and the factors associated with such
outcomes.
• Example- what is the prevalence of diabetes in
this community?
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9. Case-control study
• It is to compare the individuals who have the
outcome(cases) with the individuals who do
not have the outcome(control) according to
past history of exposure to a factor.
• More practical for detecting causes in
epidemiological research
• Appropriate for rare outcomes and when
there is reliable evidence of past exposure
• Example- study between tobacco smoking
and lung cancer3
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11. Cohort study
• The subjects are followed over time, which begins with
individuals who are exposed and not exposed to a
factor and then evaluate the subsequent development
of outcomes
• Longitudinal study allowing us to study changes and
establish the time sequence in which things occur.
• It is possible to detect causality.
• Either prospective or retrospective
• Confounding issues
• Appropriate when good evidence on an association
between exposure and outcome.
• Outcome is not too rare
• Example- Breast feeding reduces the risk of child
obesity4
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15. Summary
• Due to the limitations in carrying out RCTs in
surgical investigations, observational studies
are becoming more popular to investigate the
relationship between exposures, risk factors.
• Recognizing that well-designed observational
studies can provide valid results is important
among the plastic surgery community
• The investigator planning an observational
study can certainly use the STROBE
statement as a tool
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16. References
1. Chung KC, Swanson JA, Schmitz D, et al. Introducing
evidence-based medicine to plastic and reconstructive
surgery. Plast. Reconstr. Surg 2009;123:1385–1389.
[PubMed: 19337107]
2. Hulley, SB.; Cummings, SR.; Browner, WS., et al.
Designing Clinical Research: An Epidemiologic
Approach. 2nd Ed. Lippincott Williams & Wilkins;
Philadelphia: 2001. p. 1-336.
3. Chung KC, Burns PB. A guide to planning and
executing a surgical randomized controlled trial.
J.Hand Surg. [Am] 2008;33:407–412.
4. Benson K, Hartz AJ. A comparison of observational
studies and randomized, controlled trials. N.Engl. J.
Med 2000;342:1878–1886. [PubMed: 10861324]
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