Cohort Study and Relative risk

Question 1

What is a cohort study?

Answer 1

• Observational study
• Investigator determines the exposure status of subjects and then follows them for subsequent outcomes
• Information about the exposure status is determined BEFORE the observation of disease status (prospective)

Question 2

What is a retrospective cohort study?

Answer 2

• A type of cohort study which utilizes historical information on exposure status and subsequent outcomes

Question 3

What is used to measure the associated between exposure and disease in cohort studies?

Answer 3

• The risk ratio (AKA relative risk)

Question 4

How do you calculate the risk ratio?

Answer 4

Risk of the exposed / Risk of unexposed

• Where risk of exposed = exposed persons with outcome / all exposed
• And risk of unexposed = unexposed persons with outcome/ all unexposed

Question 5

What is the difference between a prospective and retrospective cohort study?

Answer 5

• Prospective: Exposure to the risk factor and subsequent health outcomes are determined after the start of the study
• Retrospective: Uses information on prior exposure to risk factors and subsequent disease status

Question 6

What are some disadvantages of cohort studies?

Answer 6

• Time consuming
• Large sample often needed
• Expensive
• Not good for rare disease
• Larger loss to follow-up
• Over time diagnostic methods change which can alter study

Question 7

What are some advantages of cohort studies?

Answer 7

• Direct calculation of risk ratio (relative risk)
• Determining temporal relationship between exposure and disease
• Can give info on multiple exposures
• Minimizes bias
• Can establish cause and effect

Question 8

What is attributable risk percent?

Answer 8

• Risk difference or excess risk
• Comparing the risk of the exposed to the risk of the unexposed to determine how much of the risk is attributable to the exposure being studied
  = [Risk(exposed) - Risk(unexposed)] / Risk(exposed)

Question 9

What is a rate ratio? When would you use it?

Answer 9

• Similar to risk ratio but used when rates are being studied in a cohort study (ex. Mortality rate, incidence rate)
• Rate among exposed / Rate among unexposed