Cohort Studies

Question 1

Define ‘person-years’

Answer 1

The sum of the total time of everybody followed up in a study
Eg.
63 deaths per 1000 people in 1 year = 63 deaths per 1000 person-years

Question 2

Give 3 advantages of a cohort study

Answer 2

Study a range of outcomes
Good at studying rare exposures
Good for establishing temporal sequence
Better for conditions that fluctuate with age
Detailed prospective assessment of exposure, outcomes and confounders

Question 3

What is a concurrent/prospective cohort study?

Answer 3

A cohort study where data collection starts at the beginning of the study

Question 4

What is a historical/retrospective cohort study?

Answer 4

Outcome free individuals are selected from past records and data is collected using past medical records.

Question 5

What is an internal comparison in a cohort study?

Answer 5

Sub-cohorts within the study can be compared using incidence rate ratios

Question 6

What is an external comparison of a cohort study?

Answer 6

A SMR is calculated. The observed number of cases in the cohort study can be compared against the expected number of cases in the general population.

Question 7

List 3 disadvantages of cohort studies

Answer 7

Large and resource intensive
Take a long time
High number of losses through drop-outs and death
Ethical questions- (Eg. exposed to smoke wants to quit)
Not good for rare outcomes
Confounding factors can influence results

Question 8

Outline the concept of a cohort study

Answer 8

2 groups (unexposed and exposed to a given factor) are followed up over time to see whether a disease develops