Question
A prospective cohort study examined the role of smoking as a potential confounder or effect modifier of the relationship between air pollution and asthma among Los Angeles youth. Use the data below to test whether air pollution at baseline is associated with asthma.
Asthma
|
Total
| |||
Yes
|
No
| |||
High Air Pollution
|
238
|
162
|
400
| |
Low Air Pollution
|
14
|
401
|
415
| |
A. Risk of asthma among Los Angeles youth with high air pollution:
B. Risk of asthma among Los Angeles youth with low air pollution:
C. Calculate the unadjusted risk ratio
D. Provide an interpretation for the association between air pollution and asthma based on the unadjusted risk ratio:
E. Next, we will use stratification on smoking status to test if the association between air pollution and asthma is confounded by smoking status, or if there is an interaction between smoking and air pollution. Use the following two tables to calculate the adjusted risk ratios for the stratified samples.
Smokers Non-Smokers
Asthma
|
Asthma
|
S
| ||||||
+
|
-
|
Total
|
+
|
-
|
Total
| |||
High Pollution
|
174
|
135
|
309
|
High Pollution
|
64
|
27
|
91
| |
Low Pollution
|
11
|
351
|
362
|
Low Pollution
|
3
|
50
|
53
| |
F. Provide an interpretation for the association of pollution and asthma among smokers.
G. Provide an interpretation for the association of pollution and asthma among non-smokers.
H. What statistical test would you use to compare the results among smokers and non-smokers? What does the test assess?
I. Visually inspecting the RRs, does there appear to be effect modification by smoking on the association between air pollution and asthma?
Source: PH250A Problem Bank 10
