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-   -   A physician is deciding..... (https://www.usmle-forums.com/usmle-step-1-forum/2828-physician-deciding.html)

 achistikbenny 05-31-2010 11:51 PM

A physician is deciding.....

A physician is deciding whether to use a new test to screen for disease X in his practice. The prevalence of disease
X is 5%. The sensitivity of the test is 85%, and the specificity is 75%. In a population of 1000, how many patients
will have the diagnosis of disease X missed by this test?

A. 50
B. 42
C. 8
D. 4

 khushboo 06-01-2010 12:43 AM

C

is it C 8??
how many patients will have the diagnosis of disease X missed by this test?
simply they r asking about False negative....they hv given 5% prevalence rate...so out of 1000.... 50 will hv disease...means in 2*2 table we hv TP+FN=50
sensitivity=TP/TP+FN=85%
TP=85% * (TP+FN)
TP=85*50/100
TP=42
we hv TP+FN=50....so FN is 50-TP=8

 logical66 06-01-2010 03:40 AM

C Is correct: 8

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