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#1
06-19-2012
 USMLE Forums Scout Steps History: Not yet Posts: 96 Threads: 90 Thanked 7 Times in 6 Posts Reputation: 17
Epidemiology question

Any friend can help me with this:

PSA greater than 4ng/ml is considered as abnormal. This PSA serum test has a sensitivity of 80% and specificity of 90%. In a cross-sectional study, 10% of men of this age have prostate cancer. The result of a patient's PSA is 7ng/ml, what is the likelihood that this man actually has prostate cancer?

The answer is 47%. How to calculate? Thanks.

Soso

#2
06-20-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,088 Times in 1,047 Posts Reputation: 2108

Quote:
 Originally Posted by ruijunsu How to calculate?
Calculate away here:
Likelihood ratios in diagnostic testing
#3
12-22-2013
 USMLE Forums Newbie Steps History: Not yet Posts: 4 Threads: 1 Thanked 1 Time in 1 Post Reputation: 11

SO,
1. cross-sectional study, 10% of men of this age have prostate cancer
2. sensitivity= 80%--- diseased and positive for test
3. specificity= 90%--- healthy and negative for test
4. Positive predictive value=???

******************TEST************************
***************+************** -********
******** + **** 80 TP ********* 20 FN ******* Diseased =100 (10%)
Disease
******** -*****90 FP ********* 810 TN*******Healthy =900

****************************************** TOTAL =1000

Positive predictive value = TP/TP+FP
= 80/170
= 47%

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