fana
Forum Newbie
Topics: 2
Posts: 6
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Assuming the use of 2 standard deviations to establish reference interval of a test,what is the approximate percent chance that a normal person could have atleast one false -positive test result if two tests r ordered?
A-5%
B-10%
C-15%
D-20%
E-30%
Plz explain ur answer too.
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| docofthebigapple
Forum Senior
Topics: 23
Posts: 174
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click link below to see the answer.
http://www.prep4usmle.com/community/topic11381.ht...
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| amitjosh
Forum Senior
Topics: 9
Posts: 116
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Hi Fana,
Just consider one test first.
The probability that the result is false positive is 5% since we are considering 2SDs.
Hence the probabilty that the result is NOT FALSE POSITIVE is 95%.
Now consider the second test alone.
By the same token, the probability that the result is NOT FALSE POSITIVE is 95%.
So, now since these are two independent tests, the probability that there is NO FALSE POSITIVE is 95% x 95% = 90.25%
So, the probability that there is at AT LEAST FALSE POSITIVE is (100-90.25)% = 9.75%
I tried to put it in the most simple words I could but am sorry if it still feels complicated.
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