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Old 12-24-2011
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Default Differenece between Confounding & Effect Modification

What's the difference between confounding and effect modification ?
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Old 12-24-2011
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effect modification is when the effect of the main exposure on the outcome is modified by the level of another variable.
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Old 12-24-2011
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Default Still confused !!!

yeah that's what's written as an explanation in UW but it seems to be close to the definition of confounding ?!!!
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Old 12-24-2011
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Quote:
Originally Posted by dr-ahmed View Post
yeah that's what's written as an explanation in UW but it seems to be close to the definition of confounding ?!!!

Confounding occurs when a factor other than the one you are studying is associated both with the disease and the factor you are studying.

Imagine you are studying the association between an exposure and a disease, for example between drinking coffee and heart disease, and want to decide whether it is a causal association.

Hypothesis = coffee drinking increases the risk of heart disease

- For example, if drinking coffee is associated with smoking (perhaps people who drink coffee also tend to smoke) the smoking forms a confounding variable because we know that it independently affects heart disease. The result is that there appears to be an association between coffee drinking and heart disease when, in reality, this may be occurring just because the people who drink coffee also smoke, and it is their smoking (not the coffee drinking) which actually causes the heart disease.

Effect modification or interaction: occurs when the effect measure depends on the level of another factor or = when our chosen summary of association differs in different strata.

"The relative risk of ischemic stroke for non-whites compared with whites is about 2 for those aged 35 to 64 years and about 1 for those 65 years of age and above"

Here we have 2 strata (levels):
1.- "young 35-64y/o" = RR of ischemic stroke for non-whites compared with whites is 2
2.- "old >64" y/o" = RR of ischemic stroke for non-whites compared with whites is 1

This is an example of modification of the effect of race by age.
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The above post was thanked by:
donofitaly (12-29-2011), dr-ahmed (12-24-2011), jahn77 (12-25-2011), LEE WON HYUK (05-22-2013), md12 (12-27-2011), pass7 (12-24-2011)
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well said!! it makes sense!! thank you
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