Table 1. Urbanicity of residence and 5-year survival among prostate cancer patie
ID: 3221791 • Letter: T
Question
Table 1. Urbanicity of residence and 5-year survival among prostate cancer patients enrolled in a retrospective cohort study
5-Year Survival
Urbanicity
Yes
No
Total
Urban
2,829
3,553
6,382
Rural
321
797
1,118
Calculate and interpret the relative risk.
Now consider the same data stratified by 5-year age groups.
Table 2. Urbanicity of residence and 5-year survival among prostate cancer patients enrolled in a prospective cohort study, stratified by age
5-Year Survival
Yes
No
Total
Ages 70-74
Urban
1,597
1,717
3,314
Rural
220
434
654
Ages 75-79
Urban
1,232
1,836
3,068
Rural
101
363
464
Calculate and interpret the stratified relative risks. Is the relationship between urbanicity and 5-year survival confounded by age? Please explain and show all work.
5-Year Survival
Urbanicity
Yes
No
Total
Urban
2,829
3,553
6,382
Rural
321
797
1,118
Explanation / Answer
For Table 1:
a = 2,829, b = 3,553, c = 321, d = 797
Relative risk = [a/(a+b)] / [c/(c+d)]
= [2829/(2829+3553)] / [321/(321+797)] = 1.543878
Interpretation: As the relative risk is greater than 1, the probability for 5-year survival among prostate cancer patients in urban areas is greater than that in rural areas.
For table 2. Ages 70-74
a = 1,597, b = 1,717, c = 220, d = 434
Relative risk = [a/(a+b)] / [c/(c+d)]
= [1597/(1597+1717)] / [220/(220+434)] = 1.432543
Interpretation: As the relative risk is greater than 1, the probability for 5-year survival among prostate cancer patients of age 70-74 in urban areas is greater than that in rural areas.
For table 2. Ages 75-79
a = 1,232, b = 1,836, c = 101, d = 363
Relative risk = [a/(a+b)] / [c/(c+d)]
= [1232/(1232+1836)] / [101/(101+363)] = 1.844811
Interpretation: As the relative risk is greater than 1, the probability for 5-year survival among prostate cancer patients of age 75-79 in urban areas is greater than that in rural areas.
As the relative risk is greater than 1 for both the age group, the probability for 5-year survival among prostate cancer patients of both age group 70-74 and 75-79 in urban areas is greater than that in rural areas.
So, the relationship between urbanicity and 5-year survival is not confounded by age.
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