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19 Cards in this Set
- Front
- Back
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define prevalence
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the % of people with the disease in a population
# ppl w/ dz according to gold standard // all ppl in population |
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define sensitivity
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probability that given the dz, the pt will have a positive test
# with positive test (true positives)//# with dz |
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define specificity
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probability that a pt w/o dz will have a negative test
# with negative test (true neg)//# w/o dz |
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define PPV
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proportion of ppl with dz given a (+) test
# with dz/ all with a (+) test |
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define NPV
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proporiton of those without dz, given (-) test
post-test probability of no dz with a negative test # without dz/ all with a (-) test |
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post test probability of disease given a negative test...calculate
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this is not the NPV
#ppl with dz// # w/ (-) test NPV = # ppl w/o dz// # w/ (-) test |
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calculate LR+ from sensitivity and specificity
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LR + = sensitivity / 1-spec
(# (+) test/ # dz)// 1- ((-) test/no dz)) |
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calculate LR - from sensitivity and specificity
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LR- = 1-sensitivity/specificity
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what does LR + mean in words?
LR+ of what range makes large and consclusive increases in the likelihood of disease? insignificant increases? |
how much a + test increases the likelihood of disease
LR + > 10 LR (1-2) |
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calculate LR + and LR-
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LR + = given dz, test +/ given no dz, test +
LR - = given dz, test -/ given nodz, test - |
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post test probability of disease given a negative test...calculate
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this is not the NPV
#ppl with dz// # w/ (-) test NPV = # ppl w/o dz// # w/ (-) test |
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calculate LR+ from sensitivity and specificity
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LR + = sensitivity / 1-spec
(# (+) test/ # dz)// 1- ((-) test/no dz)) |
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calculate LR - from sensitivity and specificity
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LR- = 1-sensitivity/specificity
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what does LR + mean in words?
LR+ of what range makes large and consclusive increases in the likelihood of disease? insignificant increases? |
how much a + test increases the likelihood of disease
LR + > 10 LR (1-2) |
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calculate LR + and LR-
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LR + = given dz, test +/ given no dz, test +
LR - = given dz, test -/ given nodz, test - |
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how do you go from probability to odds?
odds to probability? |
probabiliy (X%) = X/ 100-X
A: B = A/ A+B |
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which testing parameters change with prevalence and which are simply characteristics of the test itself?
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PPV and NPV depend on prevelance, so they change
sensitivity, specificity, LR+ and LR (-) are characteristics of the test itself and do not change with the pre-test probability |
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what is the best test to rule in a disease?
what is the best test to rule out a disease? |
the one with the largest LR +
the one wiht the smallest LR (-)>>the more likely that a (-) test is a true negative since : LR (-) = given dz, test (-)// given no dz, test (-) |
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in order to mulitple LR ratios to find post test probability of multiple tests, the tests must be _______
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independent of one another
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