Epdiemiology: Case Control Studies

Question 1

What is a case control study

Answer 1

Measure exposure in cases (those with disease) and controls (without disease) and then try to measure exposures in each of the groups

Question 2

Draw a case control study table then state the equations for odds in cases and odds in controls

Answer 2

Cases Controls
Exposed. A. B
Not exposed C. D

Odds in cases; A/C
Odds in controls: B/D

Question 3

How would you calculate the odds ratio in a case control study

Answer 3

Odds ratio is calculated using a cases and control table

Then calculating (A/C)/ (B/D)

Question 4

How do you interpret an odds ratio?

Answer 4

It is the risk of disease given the exposure.

Hence, so long as A/C doesnt = B/D there is an association present and the ratio isn’t equal to 1

Question 5

When would you use a case control study instead of a cohort study?

Answer 5

When there is a rare outcome
Multiple exposures
Time varying exposures

Question 6

When would you use a cohort study instead of a case control study

Answer 6

Where there is a rare exposure

It is a field study

Question 7

In a case control study how many cases would you require to investigate small effect sizes?

Answer 7

800

Question 8

Interpret these odds ratio’s

A. 3.0
B. 1.7
C. 0.8

Answer 8

A. Exposure has a 3x increase in outcome

B. Exposure has a 70% increase in outcome

C. Exposure has a 20% decrease in outcome

Question 9

Define an effect modificator

Answer 9

A factor that has different effects of exposure to a risk factor e.g dose gradient

Question 10

Give some examples of factors that can be effect modifiers

Answer 10

Genetics
Nutrition 
Disease
Age 
Gender
Physical fitness