Confounding

1
Confounding
2
Is confounding a kind of bias?

• Primary prevention
• Saturated fat intake atherosclerosis
• Secondary prevention
• High triglyceride level atherosclerosis

3
High TG
?
Low HDL
Atherosclerosis
4
Selection Bias
5
Maternal smoking
?
LBW
Mortality
6
Maternal smoking
RRU 3.2
Mortality
7
Maternal smoking
RRA ?
?
LBW
Mortality
8
Maternal smoking
RRA 1

LBW
Mortality
9
Maternal smoking
RRA 2.8
?
LBW
Mortality
10
Maternal smoking
?
LBW
Mortality
11
Maternal smoking

LBW
Mortality
12
Maternal smoking
?
LBW
Mortality
13

Unknown biologic factor(s)
C as a marker for D
14
Periodontal Disease
DAG Directed Acyclic Graph
?
Tooth loss
Diet
SES
CHD
15
Sex
?
Outdoor occupation
Malaria
16

• Is the confounding variable related to both the
  outcome and the exposure?
• Does the exposure

17

Crude
OR crude 1.71
OR 7.8
OR 5.3
18
(No Transcript)
19

Crude
OR crude
Stratified
Non-Smokers
Smokers
OR CF ORsmokers
OR CF- ORnon-smokers

• ORcrude 8.8 (7.2, 10.9)
• ORsmokers 1.0 (0.6, 1.5)
• ORnon-smoker 1.0 (0.5, 2.0)

20
No confounding not collapsible