EBIR

Question 1

What is a cohort study?

Answer 1

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

Question 2

What are the different types of cohort study?

Answer 2

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.

Question 3

How are cohort studies and RCT different?

Answer 3

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.

Question 4

When should you use a cohort study?

Answer 4

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.

Question 5

What are disadvantages of cohort studies?

Answer 5

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

Question 6

How can you measure effect in cohort studies?

Answer 6

2x2!

-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)

Question 7

How do you infer results of relative risk?

Answer 7

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