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
Continuous test result
A continuum of possible answers (still need to classify as positive or negative)
Dichotomous test result
Only two possible answers (positive or negative)
T/F: Principles of evaluation and interpretation are the same for both screening and diagnostic tests
True
Diagnostic test
- Used to confirm or classify disease status, so as to guide treatment or aid in prognosis
- In this setting, all animals are ‘abnormal’, and the challenge is to make a correct diagnosis
Screening test
Applied to apparently healthy members of a population to detect the presence of clinical disease/sub-clinical disease/disease-causing agents
Use of a screening/diagnostic test for RESEARCH
Identify and monitor research subjects
Use of a screening/diagnostic test for INTERNATIONAL TRADE
Keep infected animals out
Use of a screening/diagnostic test for SURVEILLANCE
Identify changes in disease status in a population
Use of a screening/diagnostic test for CLINICAL MEDICINE
Used for treatment and prognosis
Definition of a screening/diagnostic test
Tests provide information that aids in classifying animal(s) as having a disease (or other health-related state) or not
