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this is for all those who always got confused b/w the above 2:
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 definintly is a risk for lung cancer and DVT !!

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

Got it ??!


SEE ??!! It’s so simple.