Below is an excerpt from one of the published tables: No. of cases Person-years
ID: 3209208 • Letter: B
Question
Below is an excerpt from one of the published tables:
No. of cases
Person-years
Current smoker
128
125,138
Past smoker
283
242,916
Never smoker
596
704,023
Total
1007
1,072,077
1a) Why would the investigators choose to report person-years of observation?
a)So that only individuals who did not die during the study period are included in the analysis
b)To preserve baseline comparability of smokers and non-smokers
c)To adjust for possible confounding by age
d)To account for varying periods of observation (follow-up) among subjects.
e)To better approximate the risk ratio from the odds ratio
1b)There is evidence to indicate that excessive alcohol consumption is a risk factor for breast cancer. There is no evidence that smoking causes alcohol consumption. Further, study investigators report that alcohol consumption is associated with smoking, based on the following:
Never smokers
(N=74,068)
Past smokers
(N=24,188)
Current
smokers
(N=15,054)
Mean alcohol consumption (g/day)*
2.3
4.3
5.0
*calculated from a food frequency questionnaire in 1991.
1c) Alcohol consumption meets the criteria to potentially confound the relationship between smoking and breast cancer. (1 pt)
a)True
b)False
c)Cannot be determined from the given information
1d) The investigators reported that after controlling for alcohol consumption, the risk of breast cancer among ever smokers was 1.02 times that of never smokers (i.e. the risk of breast cancer was only 2% higher in ever smokers compared to never smokers).Based on this adjusted analysis (RR=1.02) and the crude estimate obtained above, what do you conclude about the effect of smoking on breast cancer, controlling for alcohol consumption?
a)There is no evidence for a confounding effect of alcohol consumption on the relationship between smoking and breast cancer.
b)Alcohol consumption confounded the relationship between smoking and breast cancer in a positive direction
c)Alcohol consumption confounded the relationship between smoking and breast cancer in a negative direction
d)There is a strong causal relationship between alcohol consumption and breast cancer.
e)We cannot conclude anything about the relationship between smoking and breast cancer based on the stratified analyses.
No. of cases
Person-years
Current smoker
128
125,138
Past smoker
283
242,916
Never smoker
596
704,023
Total
1007
1,072,077
Explanation / Answer
1 ans ) e)To better approximate the risk ratio from the odds ratio
2 ans a)True
3 ans ) There is no evidence for a confounding effect of alcohol consumption on the relationship between smoking and breast cancer.
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