lecture 2 - test characteristics - clinical reasoning Flashcards
What is the sensitivity of a test?
The proportion of people who have a disease that test positive (true positive)
What is the specificity of a test?
The proportion of people without a disease who have a negative test (true negative)
How is sensitivity calculated?
(true positives)/(true positives + false negatives)
How is specificity calculated?
(true negatives)/(true negatives) + (false positives)
If you want to be sure a patient doesn’t have a serious disease, is a test with high sensitivity or high specificity better?
High sensitivity (SNOUT), because the test will have very few false negatives
If you want to be sure a patient does have a disease, is a test with high sensitivity or high specificity better?
High specificity - (SpPIn), because the test will have very few false positives
Do predictive values or sensitivity/specificity depend on disease prevalence?
Predictive values
What is a positive predictive value?
The proportion of people with a positive test who are true positives
What is a negative predictive value?
The proportion of people with a negative test who are true negatives
How is the positive predictive value calculated?
(true positives)/(true positives + false positives)
How are negative predictive values calculated?
(true negatives)/(true negatives + false negatives)
How does the positive predictive value change as the disease prevalence increases?
PPV increases
How does the negative predictive value change as the disease prevalence increases?
NPV decreases
What is pre-test probability/prior estimate?
The likelihood that a patient has the condition/the prevalence of the condition in their population, if some tests have been done, then the probability that they have the condition, based on the NPV/PPV
