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22 Cards in this Set

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  • Back
What is the positive predictive value? (equation & meaning)
-If test result is positive, how likely is it that the patient actually has the disease?
-PPV= TP/ (TP + FP)
What is the negative predictive value (equation & meaning)?
If the test result is negative, how likely is it that the patient really does not have the disease?
-NPV= TN / (TN + FN)
Compare sensitivity and positive predictive value.
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?"
Compare specificity and negative predictive value.
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?"
Sensitivity and specificity are characteristics of what?
The diagnostic test
What do the positive predictive value and negative predictive value depend on?
Test validity and disease prevalence
What does it mean if a test is positive with sequential testing?
Where the test is positive on BOTH tests
- Sequential= two-stage testing
How do you calculate the net sensitivity of sequential testing?
Net sensitivity= sens1 * sens2
How do you calculate the net specificity of sequential testing?
Net specificity= spec1 + spec2- spec1* spec 2
When performing sequential testing you LOSE net _______ and GAIN net ________.
Lose net sensitivity
Gain net specificity
What is sequential testing a good method for? What is it a poor method for?
GOOD method for identifying most healthy animals
POOR method for finding all those that have a disease
Are net sensitivity and specificity of sequential testing affected by the sequence of tests?
-Might choose order of tests so as to make the group of re-tests as small as possible for cost reasons
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%?
Run the test with higher specificity first, because it excludes more negatives from the retest group
What does a positive mean with simultaneous testing?
Test positive on AT LEAST ONE test
How do you calculate the net sensitivity of simultaneous testing?
Net sensitivity: sens1 + sens2 -sens1*sens 2
How do you calculate the net specificity of simultaneous testing?
Net specificity= spec1*spec2
With simultaneous testing you GAIN net _____ and LOSE net _____.
Gain net sensitivity
Lose net specificity
What is the net effect of simultaneous testing?
Is to ask the patient to prove that it is healthy
Simultaneous testing is a GOOD method for finding what animals?
All those that have a disease
Simultaneous testing is a POOR method for what?
Finding all the healthy animals
The error rate of sequential or simultaneous testing depends on what?
The prevalence of the disease being screened for
- high prevalence--> low sensitivity means lots of errors
-Low prevalence--> low specificity means lots of errors
The repeatability of tests can be compromised by what 3 things?
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