Lecture 27 - Confounding

Question 1

What are confounders?

Answer 1

multiple factors confused with the effect of something else

Question 2

What are the properties of a potential confounder?

Answer 2

1. Independently associated with
   the outcome
2. Independently associated with
   the exposure
3. Not on the causal pathway

Question 3

What can confounding do?

Answer 3

• over/underestimate association
• change the direction of the true association
• give appearance of association when there isn’t one

Question 4

How do we get information of confounders?

Answer 4

• Use literature to identify known and suspected risk factors for outcome
• Collect information on factors strongly associated with exposure, regardless if known risk factor

Question 5

How do we control confounding?

Answer 5

• randomisation (only RCTs)
• restriction
• matching

Question 6

What is restriction?

Answer 6

All attempt to make groups being compared alike with regard to potential confounder

Question 7

What are stratum?

Answer 7

level/category of factor e.g age range

Question 8

What is matching?

Answer 8

Each case matched with one or more controls having the same confounding variable characteristic

Question 9

What are the benefits of matching?

Answer 9

• Useful for difficult to measure/complex potential
  confounders
• Can improve efficiency of case
  -control studies with small numbers

Question 10

What is not good about restriction?

Answer 10

• Works best with large sample size
• Need equipoise
• Need intention to treat analysis

Question 11

What is not good about matching?

Answer 11

• Individual matching can be difficult and limit number of potential participants
• Need special matched analysis for individual matching