Cohort Studies

Question 1

advantages of cohort studies

Answer 1

• exposure precedes outcome since cohort is disease-free at baseline
• no recall bias
• can study multiple outcomes associated with rare exposures
• can estimate all measures of incidence and effect

Question 2

disadvantages of cohort studies

Answer 2

• requires large investment of time, human and financial resources
• requires large sample sizes
• reproducibility is hard
• loss to follow up
• inefficient for studying rare diseases
• uncontrolled confounding

Question 3

what are the possible biases in cohort studies?

Answer 3

• selection bias (initial cohort is not representative of the underlying population)
• information bias (misclassification of exposure or outcome)
• confounding (unmeasured day to day variables)

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Question 4

how can exposure be measured in cohort studies?

Answer 4

questionnaires

lab tests/physical measurements

medical records

occupational records

civi/governmental records

Question 5

advantages of retrospective cohort studies over prospective?

Answer 5

• less time consuming
• faster answers
• cheaper
• don’t have to employ people for regular follow up

Question 6

what are cohort studies used for?

Answer 6

• to measure infrequent/unusual exposure (e.g. radiation_
• to study multiple outcomes related to infrequent exposure
• to measure a rare outcome
• to establish temporal sequences
• if you are interested in measuring risk over time

Question 7

give an example of a prospective cohort study.

Answer 7

Framingham study on cardiovascular outcomes

Designed to study the effect of multiple factors on coronary heart disease (cholesterol, systolic BP etc).

From this, the Framingham cardiovascular risk score was developed.

Question 8

give features of prospective cohort studies.

Answer 8

• measure risk factors ‘today’, follow-up
• can be followed up to any point in future
• records must be well maintained for both exposure groups

Question 9

give an example of a retrospective cohort study

Answer 9

asbestos exposure - mesothelioma

Question 10

Name features of a retrospective cohort study.

Answer 10

• outcome of interest is examined ‘today’, history of exposure determined from health, civic records
• records must be obtained with same level of detail for both outcome groups
• can identify a cohort/determine exposure and continue to follow-up

Question 11

what are the disadvantages of prospective cohort studies?

Answer 11

• time consuming
• expensive
• loss to follow up
• recall bias
• can’t measure rare outcomes

Question 12

give advantages of prospective cohort studies

Answer 12

• defined cohort - detailed exposure records

Question 13

give advantages of retrospective cohort studies

Answer 13

faster answers

don’t have to employ people for regular follow-ups - cheaper

Question 14

give disadvantages of retrospective cohort studies

Answer 14

• quality of records has to be checked

Question 15

how can exposure be measured in a cohort study?

Answer 15

• questionnaires
• lab tests / physical measurements
• medical records
• occupational records
• civic / governmental records

Question 16

how can outcomes be measured in cohort studies?

Answer 16

• clinical assessment
• questionnaires
• medical records
• civic / governmental records