Musuq
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The graph shows the population distribution for values obtained from a test on a group of healthy and diseased persons. A, B, C, D, and E represent various decision points for determining distinctions between diseased and normal populations. Which cut-off point will give a specificity of 100%?
A. A
B. B
C. C
D. D
E. E
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| smal
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C
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| Allison
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Answer E Specificity: the probability of correctly identifying disease-free persons.
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| Allymd
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It is C
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| pocim80
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 answer E
source - Kaplan Review book.
C is a maximal sensitivity cut off point
D is a maximal accuracy cut off point
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| IceAge
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Here is someting I found in a molecular research talk:
Sensitivity = probability that the test is positive, given the pt is positive (for the disease)
Specificity = probability that the test is negative, given the pt is negative
PPV = probability that the pt is positive, given the test is positive
NPV = probability that the pt is negative, given the test is negative
I found this to be the best explaination and easiest to remember ... hope it helps you all too.
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| mediocre
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thanx iceage .....good one
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| Addicudo
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Its E .. Look it up in Kaplan .. its Given there ..
The question asks about Specificity .. As Iceage said
Sensitivity = probability that the test is positive, given the pt is positive (for the disease)
therefore .. after point E in the graph .. IT is 100% sure that the individual is diseased .. !!
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| jamdoc
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E
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| smal
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ya E,re-read to understand.
thanks guys
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| vallia
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I don't get it...specificity is correctly identifying the normal population. specificity of 100% is where 100% are normal, thats to C point. Please explain
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| biotae
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Vallia, you seem to misunderstand the meaning of the chart. Note that X axis is the range of value for a particular test. Above the cut off value will be regarded as having disease, while below it will be thought as normal. Then what would you pick for cut off value? If you pick C, patients with test result between C and E will be regarded as having disease though they are normal, i.e., false positive. To make specificity 100%, false positive should be zero.
For your reference, To make sensitivity 100%, false negative should be zero, which means that all the diseased should have positive results. Then you have to pick C for cut off value.
I hope my explanation could be helpful.
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| NE
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A teacher said something like - you can "talk with the test" and tell it "Give me ALL the health" ( and this means Sp 100%); it's about what test can do. All the health in this case means A-E.
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