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#1




The probability that both first and repeated tests are correct?
NOTE: this is a USMLE Consult"inspired" question, so look away if you plan on using USMLE Consult as a measure of your progress.
 The result of a diagnostic test is negative. The physician orders a retest, which also is negative. The characteristics of the test used in the physician's practice population are shown below. What is the probability that both tests are correct? Test characteristics Sensitivity = 85% Specificity = 60% Positive predictive value = 68% Negative predictive value = 80% A. 4% B. 46% C. 48% D. 64% E. 72% F. 80%
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#2




Wouldn't it just be the Negative Predictive Value which is 80% .. That means that the probability of a Negative test actually being a true negative is 80% OR the probability of the patient not having the disease if she gets a negative test result would be 80%.
I would go with F) 80% ... 
#3




interesting question. I would also go with E), but a part of me thinks that performing the test twice would change something..
what is the answer? 
#4




isnt this sort of a probability question?
"BOTH are correct", so X AND Y are correct, so you MULTIPLY the probabilities X is specificity, and Y is NPV so 60% * 80% = 48% (ANSWER C) I have no clue what i just did, but that number came up in my head and its on the answer list, so i thought i'd throw it in here... Last edited by Renaissance; 04092012 at 01:58 AM. 
#5




I think its D 64%
they are asking about the negative predictive value of the test. since it was done 2 times .... so the probability of them both being correct would be 0.8*0.8 = 0.64 or 64% i may be wrong here 
The above post was thanked by:  
Dr.NickRiviera (04092012) 
#6




that makes sense

#7




answer = D
the answer is 64%
NPV x NPV 0.8 x 0.8 0.64
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The above post was thanked by:  
dr.morphine (04092012) 
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BiostatisticsEpidemiology, Step1Questions 
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