Suppose that 100,000 men were screened for prostate cancer for the first time us

Question

Suppose that 100,000 men were screened for prostate cancer for the first time using a blood test. Of these, 4,000 men had a positive result on the screening blood test; of those who tested positive, 900 had a biopsy indicating a diagnosis of prostate cancer. Among the remaining 96,000 men who screened negative, 250 developed prostate cancer within the following year and were assumed to be false negatives to the screen.

a) Fill in the 2X2 table below showing these results (all 9 cells) True Disease Status Test result Disease + Disease - TOTAL Test + 4000 Test - TOTAL
b) Calculate and interpret the sensitivity and specificity of the screening test. Report as a percent and include 1 decimal point

c) Calculate and interpret the predictive value positive (PVP) and predictive value negative (PVN) of the screening test. Report as a percent and include 1 decimal point d) There is a widespread assumption that screening a population to detect the early stages of disease is always beneficial. However, there are risks and costs that must be weighed against the benefits of screening. Briefly describe two hidden costs of screening for prostate cancer as they relate to this problem.

Explanation / Answer

a) Disease Non disease Total

Test Result Positive 900 3100 4000

Negative 250 95750 96000

1150 98850 100,000

b) Sensitivity: 900/1150=0.7826~78.26%

Specificity: 95750/98850=0.9686~96.86%

c) PVP=900/4000=0.225~22.5%

PVN=95750/96000=0.997~99.7%

d) The test procedure are costly and time taking with real patience for follow up.

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