4.2.2. confounding classical approach
Transcript of 4.2.2. confounding classical approach
![Page 1: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/1.jpg)
Second approach: “Classical” approach based on a priori criteria
2014 Page 1
18
“Bias of the estimated effect of an exposure on an outcome due to the presence of a common cause of the exposure and the outcome” – Porta 2008
● A factor is a confounder if 3 criteria are met:● a) a confounder must be causally or noncausally
associated with the exposure in the source population (study base) being studied;
● b) a confounder must be a causal risk factor (or a surrogate measure of a cause) for the disease in the unexposed cohort; and
● c) a confounder must not be an intermediate cause (in other words, a confounder must not be an intermediate step in the causal pathway between the exposure and the disease)
![Page 2: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/2.jpg)
19
Exposure
E
2014 Page 2
Disease (outcome)D
Confounder
C
Confounding Schematic
Szklo M, Nieto JF. Epidemiology: Beyond the basics. Aspen Publishers, Inc., 2000. Gordis L. Epidemiology. Philadelphia: WB Saunders, 4th Edition.
![Page 3: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/3.jpg)
Exposure
EConfounder
C
Intermediate cause
Disease
D
20
2014 Page 3
![Page 4: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/4.jpg)
Exposure
E
ConfounderC
General idea: a confounder could be a ‘parent’ of the exposure, but should not be be a ‘daughter’ of the
exposure
Disease
D
21
2014 Page 4
![Page 5: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/5.jpg)
Example of schematic (from Gordis)
22
2014 Page 5
![Page 6: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/6.jpg)
Birth Order
E
2014 Page 6
23
Down SyndromeD
Confounding factor: Maternal Age
C
Confounding Schematic
![Page 7: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/7.jpg)
HRT use Heart disease
Association between HRT and heart disease
Confounding factor: SES
2014 Page 7
24
Are confounding criteria met?
![Page 8: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/8.jpg)
BRCA1 gene Breast cancer
Confounding factor:Age
x
2014 Page 30
25
Are confounding criteria met?Should we adjust for age, when evaluating the association between a genetic factor and risk of breast cancer?
No!
![Page 9: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/9.jpg)
Sex with multiple partners Cervical cancer
Confounding factor: HPV
Are confounding criteria met?
2014 Page 9
26
![Page 10: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/10.jpg)
Sex with multiple partners
HPV Cervical cancer
2014 Page 10
27
What if this was the underlying causal mechanism?
![Page 11: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/11.jpg)
Obesity Mortality
Are confounding criteria met?
2014 Page 11
Confounding factor: Hypertension
28
![Page 12: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/12.jpg)
Obesity Hypertension Mortality
2014 Page 12
29
What if this was the underlying causal mechanism?
![Page 13: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/13.jpg)
Direct vs indirect effects
Obesity Hypertension Mortality
ObesityIndirect effect
Hypertension Mortality
Direct effect
2014 Page 13
Direct effect is portion of the total effect that does not act via an intermediate cause 30
Indirect effect
![Page 14: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/14.jpg)
Hernan MA, et al. Causal knowledge as a prerequisite for confounding evaluation: an
appl3ic3ation to birth defects epidemiology. Am J Epidemiol 2002;155(2):176-84.
2014 Page 14
Simple causal graphs
DC E
Maternal age (C) can confound the association between multivitamin use (E) and the risk of certain
birth defects (D)
![Page 15: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/15.jpg)
34
Complex causal graphs
Hernan MA, et al. Causal knowledge as a prerequisite for confounding evaluation: an application to birth defects epidemiology. Am J Epidemiol 2002;155(2):176-84.
E DC
U
History of birth defects (C) may increase the chance of periconceptional vitamin intake (E). A genetic factor (U) could have been the cause of previous birth defects in the family, and could again cause birth defects in the current pregnancy
2014 Page 15
![Page 16: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/16.jpg)
35
Smoking
A
ECalcium
DBone
fractures
CBMI
supplementation
U
Physical
Activity
B
2014 Page 16
Source: Hertz-Picciotto
More complicated causal graphs!
![Page 17: 4.2.2. confounding classical approach](https://reader035.fdocuments.in/reader035/viewer/2022062523/58f179ee1a28ab69728b4661/html5/thumbnails/17.jpg)
The ultimate complex causal graph!
36A PowerPoint diagram meant to portray the complexity of American strategy in Afghanistan!
2014 Page 17