Cohort Studies

Question 1

How are cohort studies conducted?

Answer 1

Recruit disease-free individuals and classify them according to exposure status, follow them up over time, analyse and interpret results

Question 2

What are the advantages of cohort studies?

Answer 2

Good for rare exposures or long time disease to develop (temporal sequence)

Question 3

What are the disadvantages of cohort studies?

Answer 3

Time - lengthy, high number of losses to follow up - survivor bias, results take a long time - ethics, unknown confounders, not good for rare diseases

Question 4

What is an internal comparison?

Answer 4

Sub-cohorts within your original group and then you compare exposed and unexposed within the cohort (uses IRR)

Question 5

What is an external comparison?

Answer 5

Exposed population is compared against a reference population (uses SMR)

Question 6

What does concurrent mean?

Answer 6

Follow up starts immediately

Question 7

What does historical mean?

Answer 7

Collect follow up data from the past (could have unknown confounders)

Question 8

What are the limitations of comparison to an external cohort?

Answer 8

Limited data, often there’s no incidence data, usually have to work with mortality data, study and reference populations may not be comparable

Question 9

What is a potential problem with internal cohort studies over external cohort studies?

Answer 9

The internal cohort may be healthier than the general population and therefore not be truly reflective