POPH192 Lecture 27 - Confounding I

Question 1

what is confounding?

Answer 1

a mixing or muddling of effects when the relationship we are interested in is confused by the effect of something else - the confounder

Question 2

what are the 3 properties of a potential confounder?

Answer 2

1) independently associated with the outcome
2) independently associated with the exposure
3) not on the casual pathway

Question 3

what does it mean that the potential confounder is independently associated with the outcome?

Answer 3

• a risk/ protective factor for the outcome regardless of exposure status
  e. g sex, smoking, diet and physical activity

Question 4

what does it mean that the potential confounder is independently associated with the exposure?

Answer 4

• different proportions of people with potential confounder across exposure groups
  e. g different proportions of people with these characteristics in the exposure/control group: sex, smoking, diet and physical activity
• imbalance

Question 5

what does it mean that the potential confounder is not on the casual pathway?

Answer 5

• not the mechanism by which the exposure affects the risk of the outcome

Question 6

what is a change of direction of a true association?

Answer 6

the risk factor becomes a protective factor (an vice versa)

Question 7

what are the 2 ways to collect information on all potential confounders?

Answer 7

• property 1) use literature to identify known and suspected risk factors for the outcome
• property 2) collect information on facts strongly associated with the exposure, regardless if known as a risk factor

Question 8

what is the way to control confounding in a study design?

Answer 8

remove imbalance and make the control and the exposure groups alike on any given factor

Question 9

what is matching?

Answer 9

choose people for the comparison (control) group who have the same values of the potential confounding factor(s) as people in the exposed group (cohort studies) or case group (case-control studies)

Question 10

what is individual matching?

Answer 10

each case is matched with one or more controls having the same confounding variable characteristic(s)

Question 11

what is frequency matching?

Answer 11

matching at an aggregated level