kity
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A 55 yr old man visits his phyisicin with complain of urinary infrequency. Examination finds a 1 cm nodule on his pprostate gland. The physician orders a prostate-specific antigen serum test. By normal standard, this has a sensitivity of 80% and a specificity of 90%. A recently published epidemologic article found that in across-sectional study, 10% of men of this age have prostate cancer. the result of th patient's PSA is 7ng/ml. what is your best estimate of the likelihood that this man actually has prostate cancer?
1. 13%
2. 25%
3. 36%
4. 47%
5. 58%
6. 69%
7. 72%
8. 81%
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| robin082006
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Analyze the question firstly:
Sensitivity=80%
Specificity=90%
Prevalence=10%
Test Positive, this question did not indicate the cut off of PSA, so I suppose this is positive test.
And the question asks about Positive predictive value
Test result---------------------Disease
.....................................Yes.............No
Postive,,,,,,,,,,,,,,,,,,,,,,,,,,,8-------------9
Negative.........................2................81
Total.............................10................90
So positive predictive value=8/17=47
answer 4
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| kity
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thanx robin.
but could u pls explain how do u get 9 and 81 in the table?
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| molly
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since 10%of the people will have the disease for which the sesitivity is 80% so the true positives would be 8%(out of 10 %with disease) and 2%will be people wh have disease but didnt test positive(since sensitivity is 80%)so these are false negative..
now sincee 10 %have disease so 90%will not have the disease and the specificity is 90%so people who truly wont have he disease menas true negatives would be 90%of 90(since 10%had the disease) so the true negatives would be 81% which leaves the false positves to be 9%(90-81)
now just plug in the values in the 2 b 2 table and u will ge t he PPV...WHICH WILL BE 47%
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