hopdoc
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A 55 yo male complains of urinary infrequency. 1 cm nodule found on prostate gland. PSA ordered. By common standards, a PSA level greater than 4ng/ml considered abnormal. Using this standard, this test has a sensitivity of 80% and a specificity of 90%. A recently published epidemiologic article found that in a cross-sectional study, 10% of men of this age have prostate cancer. The result on the patient's PSA is 7ng/ml. What is your best estimate of the likelihood that this man actually has prostate cancer?
A. 13%
B. 25%
C. 36%
D. 47%
E. 58%
F. 69%
G. 72%
H. 81%
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| hopdoc
Forum Senior
Topics: 14
Posts: 49
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somebody? I tried doing it using the various formulas for sensitivity and specificity but nothing works. It's from the Kaplan notes...they have given the answer but no explanation.
Anybody?
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| msyamp
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answer is 81%?
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| kingsofke
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D. 47%
Its a step1 question. Take 100 people , 10 will have Prostate CA(prevalence 10%). Test is 80% sensitive so 8 will test + and 2 will be - . Non diseased are 90. Test are 90% specific so 81 will be tested -ive but 9 will be false +ive. Likelihood is just positive predictive value of test i.e.
TP/TP + FP i.e. 8/8 + 9 nearly 47 %. (similar question is in step1 qbank. )
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| msyamp
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thank you kingsofke great explanation.
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| msyamp
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is that the given answer hopdoc?
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| hopdoc
Forum Senior
Topics: 14
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Yes it is 47%. Thank you veyr much kingsofke. That makes sense now.
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| kingsofke
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you are wellcome 
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