Question

6. Prostate-specific antigen (PSA) test measures the level of PSA in a man’s blood and is widely used to screen for prostate cancer. A study was conducted to determine the diagnostic utility of PSA density in detecting clinically significant prostate cancer among 2162 men who underwent prostate biopsy. Among the 499 men known to be attacked with prostate cancer, 189 had a positive test Among the 1663 men designated free of prostate cancer , 1400 had a positive test .Calculate & interpret the following screening test value :

A. Draw Draw 2x2 table
B. Sensitivity
C. Specificity and
D. Positive predictive value
E. Negative predictive value
F. Accuracy

Answer 1

A. The 2x2 table for the PSA test is as follows:

| Prostate Cancer | No Prostate Cancer |

Positive Test | 189 | 1400 |

Negative Test | 310 | 262 |

B. Sensitivity = (True Positive) / (True Positive + False Negative)

Sensitivity = 189 / (189 + 310) = 0.378

C. Specificity = (True Negative) / (True Negative + False Positive)

Specificity = 1400 / (1400 + 262) = 0.842

D. Positive Predictive Value (PPV) = (True Positive) / (True Positive + False Positive)

PPV = 189 / (189 + 1400) = 0.119

E. Negative Predictive Value (NPV) = (True Negative) / (True Negative + False Negative)

NPV = 262 / (262 + 310) = 0.458

F. Accuracy = (True Positive + True Negative) / (True Positive + False Positive + True Negative + False Negative)

Accuracy = (189 + 262) / (189 + 1400 + 310 + 262) = 0.465

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