Lecture 19: Cohort studies

Question 1

What is a cohort study?

Answer 1

individuals are defined on the basis of presence or absence of exposure to a suspected risk factor. They are then followed up over time to see if they develop an outcome

Question 2

What can we measure using cohort studies?

Answer 2

Incidence proportion:
Number of people who develop the disease in a specific period / Number of people at risk of developing the disease at the start of the period

Incidence rate:
Number of people who develop the disease in a specific period / Number of person-years at risk of developing the disease

Relative risk

Risk difference

Question 3

Cohort studies recap:

Answer 3

1. Identify a source population
2. Recruit your sample population
3. Assess exposure to identify which group participants belong in
4. Follow up over time
5. Observe whether or not participants develop the outcome
6. Calculate measures of occurrence and measures of association

Question 4

What is the difference between Historical Cohort study, Case control study and Cross-sectional study?

Answer 4

Historical Cohort Study:
Follows a group from past exposure to outcomes over time using historical data.

Case-Control Study:
Compares those with a disease (cases) to those without (controls) to look for past exposures.

Cross-Sectional Study:
Assesses exposure and outcome at the same time to determine prevalence or associations.

Question 5

Cohort Study: Strengths & Limitations

Answer 5

Strengths:
Determines temporal sequence between exposure and outcome.
Can examine multiple outcomes from a single exposure.
Allows calculation of incidence, relative risk, and risk difference.
Ideal for studying rare exposures.

Limitations:
Loss to follow-up can introduce bias if related to exposure/outcome.
Potential for misclassification of exposures or outcomes.
Not effective for studying rare outcomes.
Time-consuming and expensive.