Cohort studies.

Question 1

What is the best type of observational study?

Answer 1

A cohort study.

Question 2

What simple exposure category is often used in cohort studies?

Answer 2

Yes/No.

Question 3

Why is the final population in a cohort study slightly smaller than the original population?

Answer 3

Death/ loss to follow up.

Question 4

When are cohort studies particularly useful?

Answer 4

When the time period between the exposure and the disease is relatively short.

Question 5

Cut points used when categorising continuous data always need to have a biological significance. True or false?

Answer 5

False. They can be arbitrary.

Question 6

If an outcome is subjective what do you need to do when carrying out a cohort study?

Answer 6

Define this outcome upfront.

Question 7

What two types of outcomes can be measured in a cohort study?

Answer 7

1. Single/ discrete events

2. Multiple occurrence events.

Question 8

When looking at the outcome of a discrete event in a cohort study do you consider disease subtypes?

Answer 8

No.

Question 9

Name two examples of discrete/single outcomes that can be looked at in a cohort study.

Answer 9

1. Mortality.

2. First occurrence of a disease.

Question 10

What transition is looked at in a cohort study when the outcome occurs multiple times?

Answer 10

The transition from healthy status to disease status.

Question 11

What needs to be uniform in exposed and non exposed individuals in a cohort study to reduce bias?

Answer 11

Measures for detecting outcome.

Question 12

Retrospective studies are much quicker to carry out than prospective studies meaning they are more often used. True or false?

Answer 12

False. They are quite rare.

Question 13

Future follow up can occur in a retrospective cohort studies although this is rare. True or false?

Answer 13

False. If this does happen this is an ambidirectional cohort study.

Question 14

Exclusion criteria of who to include in recruitment and analysis of cohort studies should be stated upfront. Name reasons why individuals may be excluded (5 things).

Answer 14

1. No histology recorded.
2. Insufficient data at endpoint.
3. Prevalence of a different disease at baseline (still recorded and used to investigate questions not related to that specific disease).
4. Factors which mean they can not be ‘at risk’ from your disease. (still recorded and used to investigate questions not related to that specific disease).
5. Questionable data.

Question 15

Are external reference groups more commonly used in prospective or retrospective cohort studies?

Answer 15

Retrospective.

Question 16

What is the equation for the 95% confidence interval for RR?

Answer 16

e^(lnRR+-(1.96x (B/A(A+B) + D/C(C+D)^1/2))

Question 17

What is the equation for attrituble risk?

Answer 17

Incidence in exposed- Incidence in unexposed.

Question 18

What sort of regression can adjust for potential confounding in cohort studies?

Answer 18

Multiple logistic regression.

Question 19

What sort of regression is used in survial analysis?

Answer 19

Cox proportional hazards regression- time to event used as the dependant variable.

Question 20

What is information bias?

Answer 20

When different quality and/or quantity of information is collected from the exposed/non exposed group.

Question 21

What would you call this type of bias?

’ Misclassification of exposure or disease status.’

Answer 21

Misclassification bias.

Question 22

What would you call this type of bias?

‘Individuals who partake in trials tend to be more affluent and health conscious than the average person from your population meaning they can be unrepresentative of the population as a whole’.

Answer 22

Healthy worker effect selection bias.

Question 23

What sort of validity is affected if the healthy worker effect bias is present?

Answer 23

External validity effected (Internal is not).

Question 24

Are cohort studies good for rare diseases?

Answer 24

No.

Question 25

Cohort studies should not be used if the exposure changes over time. True or false?

Answer 25

Yes, they can be. This is a disadvantage of cohort studies.

Question 26

Can both survival curves and hazard ratios be calculated from cohort studies?

Answer 26

Yes.

Question 27

What is an advantage of using observational studies?

Answer 27

They do not have the same ethical concern as analytical studies.

Question 28

Can you use case control or cohort studies be used to prepare for RCT’s?

Answer 28

Cohort.

Question 29

What sort of bias is reduced in cohort studies compared to case control studies?

Answer 29

Survival bias.

Question 30

What is guaranteed in cohort studies (and not in case control)?

Answer 30

Exposure occurring before disease status.