CONFOUNDING

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CONFOUNDING

• By ZIBA RAHBAR

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????? ?????

• ?? ?????? ????? ?? ?? ????? ? ??? ?? ???? ????
  ????? ??? ? ?????? ????.
• ?? ???? ?? ????? ??????!

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Confounder

• A B
• X

Known Risk factor
Associated, But not result Of A
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Confounder

• A. causal
• Coffee pancreatic cancer
• ( observed association )
• B. Due to confounding
• Coffee pancreatic cancer
• ( observed association )
• smoking

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example

• An unmatched case-control

Odd ratio 3082/7018 1.95
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Is this association a causal one ,or it could be
confounded by AGE!?!
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Distribution of cases controls by age
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Relation of exposure to age
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Approach! a stratified analysis with subjects in
two age group.
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Hoh!

• The reason of having odd ratio 1.95?
• Because there was a difference in age
  distributions between the cases controls.
• in this eg. Age is a CONFOUNDER!!!

DROW ME THE SCHEMATIC PRESENTATION OF THIS
CONFOUNDER!
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Approaches to handling confounding

• In designing and carrying out the study
• Individual matching
• Group matching
• In the analysis of data
• Stratification
• Adjustment

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????????? ??? ????? ?????

• ??? ??????matching
• ??? ??????stratification

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• ( ???????? ?? ????? ????????? ???? ???? ????. )

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??!

• ????? ??? ?????
• ??????
• Stratification ????? ???? (????? ?????)
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  ????? ????? ???? ????? ??? ?? ?????? ?? ?????/
  ????? ?? ??? ?????? ????.

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???? ???!

• ????? ????? ????
  bias
• ?????? ????.
• ???? ??? ?? ?? ???? ????? ?? ????? ????? ??????
  ?? ???? ???!! bias

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MrC bcp!