epi 7 Flashcards
Sequential testing
Use two tests in a series:
First test: high sensitivity
Second test: high specificity
When to use a specificity test
When the cost of the false positive is high (ie: when a positive diagnosis would have a very poor prognosis or entail expensive treatment)
When to use a sensitivity test
When the cost of the false negative is high (ie: a test that you would use to ensure that imported animals are not infected with a disease)
Specificity can be low when….(2)
1) There is cross-reactivity (one thing is mistakenly identified as another)
2) Samples are contaminated
Specificity (Sp)
The proportion of non-diseased animals that the test correctly classifies as negative
Sensitivity can be low when….(2)
1) There are very few/small amounts of whatever the test measures
2) Samples are degraded before testing
Sensitivity (Se)
The proportion of diseased animals that the test correctly classifies as positive
We determine specificity by using it to test a group of _______ animals
Non-diseased
We determine sensitivity by using it to test a group of _______ animals
Diseased
False positive
Non-diseased animal that tests positive
False negative
Diseased animal that tests negative
True negative
Non-diseased animal that tests negative
True positive
Diseased animal that tests positive
Gold standard test
Accurate, reliable tests
But often very labor intensive, impractical, highly invasive, slow, and/or expensive
Continuous tests: How is the decision made?
1) Test a group of animals that HAVE the disease (using gold-standard test) = DISEASED INDIVIDUALS
2) Test a group of animals that do not have the disease (using gold-standard test) = NON-DISEASED (‘HEALTHY’) INDIVIDUALS
3) Define a cut-off value that best separates the two groups
