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22 Cards in this Set
- Front
- Back
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What is the positive predictive value? (equation & meaning)
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-If test result is positive, how likely is it that the patient actually has the disease?
-PPV= TP/ (TP + FP) |
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What is the negative predictive value (equation & meaning)?
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If the test result is negative, how likely is it that the patient really does not have the disease?
-NPV= TN / (TN + FN) |
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Compare sensitivity and positive predictive value.
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Sensitivity asks, "given the patient has a disease, how likely is it that the test finds it?"
PPV asks: "given the patient tested positive, how likely is it that it actually has the disease?" |
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Compare specificity and negative predictive value.
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Specificity asks: "given that the patient is healthy, how likely is it that the test confirms this?"
NPV asks: "given that the patient tested negative, how confident can I be that it really doesn't have the disease?" |
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Sensitivity and specificity are characteristics of what?
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The diagnostic test
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What do the positive predictive value and negative predictive value depend on?
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Test validity and disease prevalence
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What does it mean if a test is positive with sequential testing?
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Where the test is positive on BOTH tests
- Sequential= two-stage testing |
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How do you calculate the net sensitivity of sequential testing?
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Net sensitivity= sens1 * sens2
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How do you calculate the net specificity of sequential testing?
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Net specificity= spec1 + spec2- spec1* spec 2
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When performing sequential testing you LOSE net _______ and GAIN net ________.
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Lose net sensitivity
Gain net specificity |
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What is sequential testing a good method for? What is it a poor method for?
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GOOD method for identifying most healthy animals
POOR method for finding all those that have a disease |
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Are net sensitivity and specificity of sequential testing affected by the sequence of tests?
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No
-Might choose order of tests so as to make the group of re-tests as small as possible for cost reasons |
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How can you choose the order of sequential tests to make the group of re-tests as small as possible, therefore reducing cost with a disease that has a prevalence <50%?
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Run the test with higher specificity first, because it excludes more negatives from the retest group
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What does a positive mean with simultaneous testing?
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Test positive on AT LEAST ONE test
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How do you calculate the net sensitivity of simultaneous testing?
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Net sensitivity: sens1 + sens2 -sens1*sens 2
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How do you calculate the net specificity of simultaneous testing?
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Net specificity= spec1*spec2
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With simultaneous testing you GAIN net _____ and LOSE net _____.
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Gain net sensitivity
Lose net specificity |
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What is the net effect of simultaneous testing?
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Is to ask the patient to prove that it is healthy
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Simultaneous testing is a GOOD method for finding what animals?
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All those that have a disease
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Simultaneous testing is a POOR method for what?
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Finding all the healthy animals
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The error rate of sequential or simultaneous testing depends on what?
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The prevalence of the disease being screened for
- high prevalence--> low sensitivity means lots of errors -Low prevalence--> low specificity means lots of errors |
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The repeatability of tests can be compromised by what 3 things?
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1) Intrasubject variation
- Need to standardize conditions under which test is administered 2) Intraobserver variation -Need to follow standardized protocols in interpreting tests 3) Interobserver variation -important when in a multidoctor practice |
