Questions and Answers
What is the purpose of conducting a cohort study?
What is the characteristic of subjects in a cohort study?
What is the main advantage of conducting a cohort study?
What is the term 'cohort' derived from?
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What is the limitation of cohort studies?
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What is the advantage of cohort studies over clinical trials?
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What is the purpose of following two groups of individuals in a cohort study?
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When are cohort studies used?
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What is the primary goal of epidemiology in a cohort study?
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What is the main difference between prospective and retrospective cohort studies?
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What is the purpose of a cross-section study in a cohort study design?
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What is a characteristic of a retrospective cohort study?
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What is an advantage of a cohort study?
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What is a limitation of a retrospective cohort study?
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What is a limitation of cohort studies?
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What is the main difference between experimental and cohort studies?
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What is the purpose of ensuring that the outcome is not present at the start of a cohort study?
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What is the purpose of a two-by-two table in a cohort study?
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What is an advantage of a retrospective cohort study?
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What is the term for the group of participants who do not have the exposure at the baseline in a cohort study?
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What is a measure of incidence in a cohort study?
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What can be calculated from the incidence measures in a cohort study?
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Why are cohort studies useful for studying rare exposures?
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What is a potential problem in cohort studies?
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What is the definition of risk in epidemiology?
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What is the formula for calculating the risk for exposed individuals?
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What is the unit of time used to measure person-time in a rate calculation?
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What does a rate measure in epidemiology?
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What is the interpretation of a relative risk (RR) equal to 1?
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What does a relative risk (RR) greater than 1 indicate?
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What is the purpose of calculating the relative risk (RR) in cohort studies?
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What is the formula for calculating the relative risk (RR)?
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Study Notes
What is a Cohort Study?
- A type of non-experimental or observational epidemiologic study design used to inform patients, clinicians, and policy makers on various topics.
- The term "cohort" refers to a group of people who have been included in a study based on a definition decided by the researcher.
Purpose of Cohort Study
- To evaluate a possible association between exposure and outcome by following two groups of individuals (exposed and unexposed) over a period of time.
Key Characteristics of Cohort Study
- Subjects should not have the outcome variable (disease free) on entry and should have the potential to develop the outcome.
- The incidence of disease among the exposed and unexposed groups are determined and compared.
General Design Framework of Cohort Study
- Selection of sample from population or self-allocated groups.
- Measuring the exposure variable in the sample.
- Ensuring that the outcome is not present (none of the participants have the disease).
- Follow-up of the different exposure groups for a period of time.
- Measurement of the occurrence of the outcome variable in each group.
Exposure Evaluation in Cohort Study
- The exposure status can have two levels: the exposed group and the unexposed group.
- A central goal of epidemiology is to identify causes (or exposures) that can explain outcomes such as disease occurrence, which are referred to as the outcome or disease.
Outcome Evaluation in Cohort Study
- A cohort study can examine the effect of an exposure on more than one outcome.
- The outcome or disease is referred to as the outcome variable.
Types of Cohort Studies
- Prospective cohort study: the study follows the participants from the start of the study.
- Retrospective cohort study (Historical Cohort): exposure and outcome have already occurred at the start of the study.
- Retrospective-prospective study: a cohort study that combines both retrospective and prospective data.
Advantages and Strength of Cohort Study
- Knowing that predictor variable was present before outcome variable occurred (some evidence of causality).
- Valuable in studying rare exposures.
- 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 Study
- Expensive and inefficient for studying rare outcomes.
- A large number of subjects is usually needed.
- Often need long follow-up period or a very large population.
- Loss to follow-up can affect validity of findings.
Analytic Framework of Cohort Study
- Two-by-two tables are generally used to organize the data from a cohort study to estimate the effect of exposure on the outcome.
Measures of Incidence in Cohort Study
- Risks and rates can be further manipulated to provide additional information on the effects of the exposure of interest.
- Risk is defined as the number of new cases divided by the total population-at-risk at the beginning of the follow-up period.
- Rate is the number of new cases of an outcome divided by the total person-time-at-risk for the population.
Relative Risk (RR) or Risk Ratio
- Used in cohort studies to estimate the strength of the association between exposure and outcome.
- RR=1 indicates that the exposure is not associated with the outcome.
- RR>1 indicates that the exposure increases the risk for the outcome (risk factor).
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Description
Learn about cohort studies, a type of non-experimental research design, and how it helps establish causal links between exposure and outcome. This quiz tests your understanding of the concept and its applications.