Cohort Studies

Question 1

Kinds of frequent epidemiological studies

Answer 1

Cross-sectional studies
Case-control studies
Prospective cohort study

Question 2

Cohort definition

Answer 2

A group of people with something in common, usually an exposure or involvement in a defined population group within a defined period of time

Question 3

Characteristics cohort study

Answer 3

All of them should be at risk of developing the disease

They shouldn’t have the disease at baseline

After 1 year you classify them into ‘new incident cases’ and those who didn’t develop the disease

The exposure usually occurs prior to the beginning of the study

Question 4

Fixed cohort

Answer 4

When the cases being studied are selected at the beginning of the study - once the study starts, there is no more recruitment

Question 5

Case-cohort design

Answer 5

All the cases are included - instead of including 100% of the cohort, you select a random sample

This is done in order to cut costs

Question 6

Dynamic cohort

Answer 6

You don’t close period of recruitement (permanently open)

You can balance those who enter/and exit the study

Question 7

Uses of cohort studies

Answer 7

We study frequent outcomes (no rare diseases)

We can also study rare exposures

Relatively short induction period (period between action of risk factors and occurrence of disease)

Question 8

Advantages cohort studies

Answer 8

• Well suited to assess peculiar exposures

• You can collect multiple effects of the same exposure and also multiple exposures if planned

• The temporal sequence is adequate

• They can explain the natural history of disease

• Long latency periods

• Prevents misclassification bias

• We get direct and timely info on exposure and repeated measures

• Allows direct calculation of incidence (absolute risks)

Question 9

Disadvantages cohort studies

Answer 9

• Useless for rare diseases
• Expensive
• You need patience (not immediate results)
• Ascertainment bias
• Changes in diagnostic criteria in the long term

Question 10

Nationwide registries

Answer 10

They study the whole population of a place

Question 11

Retrospective / Historical Cohort Study

Answer 11

You start the study after the exposure and after the disease

You need to trust your registries - have very good historical records