Questions and Answers
What is the main advantage of cohort studies in establishing causality?
In a cohort study, what is the primary goal of data analysis?
What is a key limitation of cohort studies?
Why are cohort studies valuable in studying rare exposures?
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What is a key difference between cohort studies and RCTs?
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What is the primary advantage of cohort studies over RCTs?
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How are risks and rates used in cohort studies?
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What is the purpose of two-by-two tables in cohort studies?
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What is the primary goal of exposure evaluation in a cohort study?
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What is the primary objective of a cohort study in evaluating the exposure and outcome?
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What is a key advantage of retrospective cohort studies over prospective cohort studies?
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What is the purpose of a cross-sectional study in the context of a cohort study?
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What is a characteristic of a cohort study design?
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What is a key limitation of retrospective cohort studies?
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What is a limitation of cohort studies in establishing causal inferences compared to RCTs?
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What is an advantage of cohort studies over RCTs?
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What is the primary outcome of interest in a cohort study?
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What is a characteristic of the exposure in a cohort study?
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What is a key advantage of cohort studies over randomized controlled trials (RCTs)?
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What is the primary purpose of a cohort study?
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What is a key consideration in selecting participants for a cohort study?
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What is an example of a cohort study?
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What is a key characteristic of a prospective cohort study?
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Why are cohort studies often used in epidemiology?
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Study Notes
General Design Framework of a Cohort Study
- A cohort study consists of subjects at risk for a disease whose exposure status is assessed at baseline
- Subjects are followed up over time to detect incident disease
- Elements of a prospective cohort study design include:
- Selection of sample from population or self-allocated groups
- Measuring the exposure variable in the sample
- Ensuring the outcome is not present (none of the participants have the disease)
- Following up different exposure groups for a period of time
- Measuring the occurrence of the outcome variable in each group
Exposure Evaluation
- Exposure status can have two levels: exposed group and unexposed group
- Exposure evaluation typically starts with a cross-sectional study to determine baseline exposure status and exclude subjects who are not at risk for the disease
Outcome Evaluation
- A central goal of epidemiology is to identify causes (or exposures) that can explain outcomes such as disease occurrence
- Cohort studies can examine the effect of an exposure on more than one outcome
Types of Cohort Studies
- Retrospective cohort study (historical cohort): exposure and outcome have already occurred at the start of the study
- Prospective cohort study: follows subjects over time to detect incident disease
- Retrospective-prospective study: combines both retrospective and prospective data
Advantages and Strengths of Cohort Studies
- Knowing that predictor variable was present before outcome variable occurred (some evidence of causality)
- Valuable in studying rare exposures
- Can directly measure incidence of a disease outcome
- Can study multiple outcomes of a single exposure
- Relative risk (RR) is a measure of association
Disadvantages and Limitations of Cohort Studies
- Expensive and inefficient for studying rare outcomes
- A large number of subjects is usually needed
- Often need a long follow-up period or a very large population
- Loss to follow-up can affect validity of findings
Comparison with Experimental Studies
- In cohort studies, no intervention, treatment, or exposure is given to participants
- In RCTs, participants are randomly allocated to either receive the treatment/intervention or not
- In cohort studies, there is no randomization, and participants are not allocated to groups
Analytic Framework of Cohort Study
- Two-by-two tables are used to organize data from a cohort study
- Two measures of incidence are risks and rates
- Risks and rates can be further manipulated to provide additional information on the effects of the exposure of interest
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Description
Learn about the advantages and limitations of cohort studies, a research design that combines retrospective and prospective data to investigate relationships between variables and disease outcomes.