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#1
11-04-2013
 USMLE Forums Guru Steps History: Step 1 Only Posts: 340 Threads: 46 Thanked 148 Times in 85 Posts Reputation: 158
HELP TO FIGUREOUT EPIDEM. Qs

55 y o M visit his primary care physician with a complaint of urinary infrequency.examination find 1 cm nodule on his prostate gland.the physician order a PSA serum test.by common standarts a PSY level greater then 4=abnormal.using this standart test has a sensitivity 80% specificity 90%.on cross-sectional study, 10% of men of his age have prostate cancer.The result on patient PSA is 7.What si 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%

#2
11-04-2013
 USMLE Forums Guru Steps History: 1+CK+CS Posts: 359 Threads: 39 Thanked 228 Times in 135 Posts Reputation: 238

its c..47 percent..
OK here is how u solve these kinda q's..u want to calculate ppv in this q.
assume a population of 1000...acc to cs study..10% prevalence...will give u 100 diseased...
sensitivity is given 80%..so 80 will b true positive..20 will be false negative..
similarly specificity is 90...810 will be true negative..90 will be false positive..
so ppv=tp/tp+fp
=80/80+90
=47
__________________
lets do this!!
 The above post was thanked by: DrAGA (11-05-2013), step1an (11-05-2013)
#3
11-05-2013
 USMLE Forums Guru Steps History: Step 1 Only Posts: 340 Threads: 46 Thanked 148 Times in 85 Posts Reputation: 158

thanks for answer...i found it later on kaplan video lecture....thanks..i didnt know how to use 10%..lolll

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