Lecture 10-11 - Confounding & Effect Modification

Question 1

What is the counterfactual theory?

Answer 1

• using the non-exposed to attempt to see what would have happened to the exposed if they weren’t exposed (counterfactual outcome)
• requires assumption of exchangeability or comparability

Question 2

What are the three aspects of internal validity a researcher must look for before declaring the results of their research to be a “true” association.

Answer 2

• confounding/effect modification
• bias
• statistical significance

Question 3

What is confounding?

Answer 3

When a third variable distorts the association between exposure and outcome

Question 4

What are the 3 requirements of a confounder?

Answer 4

• associated with the exposure
• associated with the outcome
• not directly in the causal-pathway between exposure and outcome

Question 5

What is the visual depiction of a confounder called?

Answer 5

DAG (direct acyclic graph)

Question 6

What are the steps of testing for confounding?

Answer 6

• calculate crude (unadjusted) measure of association
• calculate adjusted measure of association for each strata of potential confounder
• take the difference between adjusted and unadjusted measure of association; if different by more than 15% there is confounding

Question 7

What is effect modification?

Answer 7

When the measure of association within the different strata of a third variable vary from one another

Question 8

What are the steps of testing for effect modification?

Answer 8

• calculate crude (unadjusted) measure of association
• calculate the measure of association in each strata
• take the difference between the highest and lowest in the strata measure of association; if different by more than 15% there is confounding