be familiar with the types of research study designs be aware of the advantages, disadvantages, and...
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Types of Research StudiesArchitecture of Clinical Research
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Be familiar with the types of research study designs
Be aware of the advantages, disadvantages, and uses of the various research design types
Recognize a study design from published study abstracts used as a class exercise
Learning Objectives
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Two main categories:1. Observational:
Studies in which subjects are observed2. Experimental:
Studies in which the effect of an intervention is observed
Studies in Medical Literature
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Case Series Case-Control Cross Sectional Cohort
Observational Studies
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Case Series◦ What are they?
Author describes some interesting or intriguing observations that occurred to a small number of patients
◦ Characteristics: The simplest design Descriptive Lead to hypotheses subsequently investigated by
other types (Case-Control, Cross-Sectional or Cohort study)
Generally over short period of time Generally no controls
Observational Studies
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Case Series & Case Reports
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Case-Control◦ Retrospective◦ Question answered: “What happened?”◦ Matching needed for controls◦ Might be difficult to differentiate from Case
Series (Both are after the fact) Ask if the goal was to describe a phenomenon, if
description is the goal Case Series
Observational Studies
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Case Control Studies
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Case-control Studies: research in reverse
Example: association between smoking and lung cancer. People with lung cancer are enrolled to form the case group, and people without lung cancer are identified as controls. Researchers then look back in time to ascertain each person's exposure status (smoking history), (retrospective design). Investigators compare the frequency of smoking exposure in the case group
with that in the control group, and calculate a measure of association.
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Cross Sectional◦ AKA Surveys, epidemiologic or prevalence
studies ◦ What are they?
Analyzes data collected on a group of subjects at one time
◦ Question answered: “What is happening now?”◦ Short time
Observational Studies
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Possible uses of Cross Sectional studies:◦ Diagnosing or staging a disease◦ Evaluating different methods of doing the same
thing e.g. Examining the relationship between histology slides
and MRI findings of diseased carotid arteries
◦ Establishing norms e.g. Establishing normal lab values from normal subjects
◦ Surveys May use preexisting validated surveys To learn what people think Sometimes combined with interviews
Cross Sectional (cont’ed)
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Cohort◦ Question answered: “what will happen?”◦ Prospective/forward◦ e.g. Framingham study of cardiovascular
disease: Started in 1948, 6000 citizens participated, followed for 20 years (study in 1970 by Gordon and Kannel)
◦ Possible uses: Typical cohort study Outcome assessment (patient outcomes:
economic, functional, satisfaction, ..) Historical Cohort studies/AKA Retrospective cohort:
Relies on prospective records collected (If accurate) – still forward in time in the past
Observational Studies
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Cohort Studies
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Both Cohort and Case-Control studies are called
“Longitudinal Studies”
Notion of time
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Observational Studies
Case Series Case-Control Cross SectionalCohort
Longitudinal Studies
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AKA Clinical Trials (Involve humans) Easier to identify (usually explicitly stated
in the abstract) Two main categories of clinical trials:
1. Controlled trials2. Uncontrolled trials
Experimental Studies
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Controlled trials– Experimental drug or procedure
compared with another, with a placebo, or with the standard procedure
– Greater validity
Experimental Studies
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Trials with independent concurrent controls◦ Double or single blind◦ Best is randomized
assignment◦ Same point in time◦ These include:
RCT: The epitome of all research
designs Provides the strongest
evidence of concluding causation
Best insurance that results are due to the intervention
Nonrandomized trials: Assignment not randomized Opened to biases
Trials with self controls◦ Subject to bias (Hawthorne
effect)◦ Can do crossover study
(with washout period in between)
Trials with external control◦ Uses the results of another
investigator’s research as a comparison
◦ Historical controls can also be used: for disease with no cures yet
Experimental StudiesControlled Trials
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The Hawthorne effect (also referred to as the observer effect) is a type of reactivity in which individuals improve an aspect of their behavior in response to their awareness of being observed.
washout period: A period in a clinical study during which subjects receive no treatment for the indication under study and the effects of a previous treatment are eliminated.
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Randomized Controlled Studies
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The Double Blind Method
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Uncontrolled trials Investigator’s experience with the new
drug or procedure is described but not formally compared with another one
More likely to be used for interventions that are procedures rather than drug
Experimental Studies
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Experimental Studies
Controlled trials Uncontrolled trials
Self controls Independent concurrent controls
External controls
RCT Non-randomized
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Systematic Reviews &Meta-analyses
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Study Pyramid
Best
Worst
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Temporal direction of study designs
Lancet 2002; 359: 57-61
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Advantages & Disadvantages
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Advantages:◦ RCT is the gold standard or reference
Disadvantages: ◦ Expensive◦ Long duration
Clinical Trials
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Advantages:◦ Design of choice for studying cause of a disease,
course, risk factors Disadvantages:
◦ Cannot be used to prove causation◦ Long studies can be costly◦ Vulnerable to patient attrition, migration
Cohort Studies
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Advantages: ◦ Quickest◦ Least expensive◦ Good for rare diseases and diseases that take
long time◦ Good for investigation of a preliminary
hypothesis◦ Time factor research
Disadvantages: ◦ Large biases◦ Difficult to find matching controls
Case-Control Studies
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Advantages: ◦ Best for:
Determining status of a disease Prevalence of disease Evaluation of diagnostic procedures
◦ Relatively quick and inexpensive Disadvantages:
◦ Provide only a snapshot in time
Cross Sectional Studies
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Advantages: ◦ Easy to write◦ May be extremely useful to investigators
looking for causes of the observation Disadvantages:
◦ Subject to many biases in patient selection◦ Should be viewed as hypothesis generating,
not conclusive
Case Series
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Thank you