35. CASE CONTROL STUDIES

Question 1

1. What kind of study is a Case Control Study?

Answer 1

• it is retrospective

RETROSPECTIVE DEFINITION:
- it deals with past events and information

Question 2

2. Who is first recruited in Case Control studies?

Answer 2

• a group of patients with a specific disease
• this is known as the Case Group

Question 3

3. Who is recruited second in Case Control studies?

Answer 3

• a random sample of individuals
• they do not suffer from the specific disease
• this is the Control Group

Question 4

4. Where do we recruit the Control Group from?

Answer 4

• they are recruited from the Source population
• from which the disease cases were derived

THEY CAN BE RECRUITED FROM:
- the general population
- this is the preferred method

THEY CAN ALSO BE RECRUITED FROM:
- the hospital
- they are the patients that are not suffering from the
disease of interest or anything similar

Question 5

5. What are the Case Group and the Control Group matched for?

Answer 5

• they are matched for key characteristics

THESE INCLUDE:
- age
- gender

Question 6

6. Why do we match the key characteristics?

Answer 6

• the aim is to eliminate any confounding from these
  factors

THE MATCHING OF THESE CHARACTERISTICS:
- is restricted to 2-3 factors
- over matching should be avoided

Question 7

7. What should we do instead of Over matching?

Answer 7

• we should adjust the potential confounders
• this would happen when we analyse the data

Question 8

8. What happens in Case Control studies after we have matched the key characteristics?

Answer 8

• we assess a series of exposures in the case and the
  control
• these exposures occurred in the past

Question 9

9. Why are Case-Control studies considered Retrospective?

Answer 9

• they start with a disease
• then they look back in time to identify the exposures

Question 10

10. What are the measures of Association related to Case-Control studies?

Answer 10

1. ODDS RATIO
   - these deal with Categorical Exposures
2. MEAN DIFFERENCE
   - these deal with Numeric Exposures

Question 11

11. What kind of outcome do we always have when dealing with Case Control Studies?

Answer 11

• a Binary Outcome

Question 12

12. What are the Descriptive Measures associated with Case Control studies?

Answer 12

• they are never calculated in this type of study
• we only look at the Analytic measures

Question 13

13. What are the 5 advantages of Case Control studies?

Answer 13

1. THEY MAKE IT POSSIBLE TO INVESTIGATE
   - the determinants of Rare Diseases
2. THEY ARE RELATIVELY EASY TO PERFORM
3. THEY ARE CHEAP
   - not as cheap as Cross-Sectional studies
4. THEY MAKE IS POSSIBLE TO ASSESS SEVERAL
   EXPOSURES
   - as well as to assess the potential confounders
   - for a single outcome
5. THEY MAKE IS POSSIBLE TO INVESTIGATE EXPOSURES
   - these exposures happened in the past
   - they happened much earlier in life related to the
   disease outcome

Question 14

14. What are the disadvantages of Case Control studies?

Answer 14

1. IF THE CONTROL GROUP IS NOT A REPRESENTATIVE
   SAMPLE FROM THE SOURCE POPULATION
   - from which the cases were derived
   - we will end up with selection bias
2. IT IS IMPOSSIBLE TO ASK THE RISK (INCIDENCE)
   - of diseases
3. IT IS VERY DIFFICULT TO PROVE CAUSALITY
   - this is due to the possible confounding
   - as well as the Bias