Epidemiologists decided to investigate the validity of new diagnostic tool for breast cancer.They used this new diagnostic tool for breast cancer in 150 women with biopsy-proven breast cancer in 300 age- and race-matched control women.The results of the new tool were positive in 136 cases and in 35 control women,all of whom showed no evidence of cancer at biopsy.Now,the epidemiologists want to use the new diagnostic tool for screening program in Cities A and B.Based on previous cross-sectional studies,the prevalence of breast cancer is 5% in City A and 1% in City B.What is the most reasonable conclusion to be drawn from these data?

A) Positive predictive value of new diagnostic tool for breast cancer in City A is higher than expected positive predictive value in City B.
B) Positive predictive values will be higher than sensitivity.
C) Positive predictive value is affected by the specificity of the test only.
D) Prevalence will not affect the positive predictive value.
E) Positive predictive value is a fixed characteristic of the test. Therefore the positive predictive value in City A will be same as positive predictive value in City B.

The sensitivity of new diagnostic test is 91%,from 136 divided by 150.The specificity of new diagnostic test is 89%,from 265 divided by 300.The positive predictive value is the number of people who test positive from people who have cancer divided by total number of people who test positive from people who have cancer and people who do not have cancer,which equals sensitivity multiplied by prevalence divided by addition of sensitivity multiplied by prevalence and 1 minus specificity multiplied by 1 minus prevalence.Therefore the positive predictive value of the test in City A is 0.30,which equals 0.05 multiplied by 0.91 divided by addition of 0.05 multiple 0.91 and 0.11 multiplied by 0.95.The positive predictive value of the test in City A is 0.01,which equals 0.01 multiplied by 0.91 divided by addition of 0.01 multiplied by 0.91 and 0.11 multiplied by 0.99."Positive predictive values will be higher than sensitivity" is not correct.Positive predictive values are lower than sensitivity."Positive predictive value is affected by the specificity of the test only" and "Prevalence will not affect the positive predictive value" are not correct.Positive predictive values are affected by sensitivity,specificity,and prevalence."Positive predictive value is a fixed characteristic of the test.Therefore the positive predictive value in City A will be same as positive predictive value in City B" is not correct; positive predictive value is not a fixed characteristic of the test.