L4 Cohort studies

Question 1

Define a cohort.

Answer 1

A group of people who share a common factor.

Question 2

Define a cohort study.

Answer 2

An epidemiological study that follows a cohort over a period of time to see how their exposures affect their outcomes.

Question 3

In a cohort study a cohort may be chosen because they represent what? (4)

Answer 3

• The general population
• Special exposure groups (e.g. smokers, uranium miners, asbestos workers with high levels of exposures, vegetarians)
• Special resource groups (e.g. physicians, civil servants, Newcastle 85+ study, Gateshead Millennium Study (new births))
• Geographically or facility-defined groups (e.g. Three Mile Island, residents near Chernobyl, hospitals with specialized maternity care).

Question 4

What are the strengths of cohort studies? (5)

Answer 4

• Clear temporal relationship between exposure and disease (certain that exposure was before disease)
• Eliminates possibility of recall bias
• Suitable for studying rare exposures if the cohort is large enough
• Can study multiple outcomes from single exposure (or multiple exposures if information is collected on these)
• Can study complex interactions between exposures.

Question 5

What are the weaknesses of cohort studies? (8)

Answer 5

• Defining and measuring exposure
• Defining and measuring disease
• Loss to follow up over long periods
• For diseases of long latency, may have to wait many years before have first study results
• Non-participation (selection) bias may affect external validity (generalizability) of results
• Very expensive
• Very time consuming
• Logistically challenging.

Question 6

Almost all exposures can be found through an ______.

Answer 6

Interview

Question 7

Why are interviews recommended wherever suitable for the measuring of exposure?

Answer 7

They are cost and time efficient and uncover almost all exposures.

Question 8

Give an example of an exposure that an interview is insufficient to uncover.

Answer 8

Genetics

Question 9

Measuring disease (or other outcomes) must be done in the same way for exposed and unexposed groups - to avoid ___1___ bias

Ideally those assessing outcomes should be blinded to exposure status of participants - to avoid ___2___ bias

Answer 9

1. Information
2. Observer