[achistikbenny]

A 55 yr old man visits his physician for urinary complaints, who finds a 1cm nodule on his prostate gland and orders PSA test. PSY > than 4ng/ml is considered abnormal by common standards. The test's sensitivity is 80%, specificity 90%. It's found that 10% of men of his age have prostate cancer on a cross sectional study. The patient's PSA is 7ng/ml. What is ur best estimate of the likelihood that this man has prostate cancer?

A. 13%
B.25%
C.36%
D.47%
E. 58%
F.69%
G.72%
H.81%

 

[drmodi44]

D.47%...??

 

[achistikbenny]

pls explain how u get ur ans. i want understand it . thank u .

 

[drmodi44]

prevalance of prostate ca. is 10%...means out of 100, 10 people r having ca.
so we hv TP+FN = 10
AND FP+TN = 90 in our 2*2 table
now test sensitivity is 80%... sensitivity=TP/TP+FN
80/100=TP/10
80/100*10=TP
TP=8
SO,FN=10-8=2
AND specificity 90%....specificity=TN/TN+FP
90/100=TN/90
90/100*90=TN
TN=81
SO,FP=90-81=9

NOW they hv asked about PPV...likelihood that pt with positive test actually hv the disease....PPV=TP/TP+FP
=8/17
=0.47
=47%

Hope this helps.....i dont know how to make table here...n m not able to attach any file...hope someone else help u making a table...

 

[achistikbenny]

thank u very much .i do understand it now. thank u very much