Confounding V/s Effect modification

Confused between confounding and effect modification?? Here is the solution:
1- Confounding bias :

Alcohol ( exposure ) Oral cancer ( outcome )
Smoking is a confounding bias here. Why ?

Because smoking is related to BOTH the exposure and the outcome. People who smoke will more often than not, also drink, and people who have oral cancer, were probably smokers ( smoking is a known risk factor for oral cancer).

2- Effect modification :

OCPs ( exposure ) Breast cancer (outcome )
Family history of breast cancer is an effect modification here.
Can you guess why ?

Asbestos ( exposure ) Lung cancer(outcome)
Smoking is an effect modification

Estrogens ( exposure ) DVT (outcome )
Smoking is an effect modification

So do you notice the difference ?? The effect modification is ONLY related to the outcome, but NOT to the exposure. Think with me here : smoking does not effect neither asbestos exposure nor estrogen levels or intake,BUT definitely is a risk for lung cancer and DVT !!

Family history of breast cancer has nothing to do with choosing to use OCPs , but definitely has a factor in increasing risk of breast cancer !!

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