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Flashcards in EBIR Deck (7):

What is a cohort study?

A study which follows a group of individuals forward through time to capture outcome.


What are the different types of cohort study?

Concurrent: Follows individuals from exposure forward until they measure an outcome.

Retrospective: Uses data (such as chart review) to identify exposure in the past, and observes outcomes.

Ambidirectional: Uses data (such as chart review) to identify exposure in the past, and continues to follow individuals forward until they measure outcome. Basically Concurrent and Retrospective combined.


How are cohort studies and RCT different?

Cohort studies are observational, and assignment of individuals into categories of "exposed" and "not exposed" is not determined by the study.

RCTs are experimental, and assignment of individuals to "exposed/treatment" and "unexposed/placebo" is determined by the study.


When should you use a cohort study?

A cohort should be used for:
(1) Examining incidence
(2) Looking at the natural history of disease
(3) Assessing the temporality of an exposure/disease relationship

Cohort studies are the only way (besides RCT) to ensure that exposure precedes disease.


What are disadvantages of cohort studies?

-Not good for rare diseases (incidence is low)
-Not good for diseases with long latent periods
-Over time you lose follow-up


How can you measure effect in cohort studies?


-Plot Disease/No Disease against Exposed/Unexposed

-Incidence in exposed = a/a+b
-Incidence in unexposed = c/c+d

Relative risk = (a/a+b)/(c/c+d)


How do you infer results of relative risk?

Relative risk = (a/a+b)/(c/c+d)

If 1.0, the exposure increases risk
If =0, there is no association between disease and exposure