Week 11: Diagnostic Validity Flashcards
What is True positive (A) False positive (B) False negative (C) True negative (D)
True positive: test shows positive when person does have condition (a)
False positive: test shows positive when person doesn’t have condition. (B)
False negative: saying you don’t have a condition when you do (c)
True negative: sayiing you don’t have a condition when you don’t (d)
Sensitivity =
Specificity =
Sensitivity =
A/ (A + C)
Specificity =
D/ (B + D)
What are the 3 statistics of diagnostic validity
- Sensitivity - true +’ve
- Specificity -proportion with the -ve result
- Likelihood ratios
What is the ideal diagnostic test
Would always correctly discriminate between those with and those without the condition
Ie
-always positive for those with the condition
-always negative for those without it
SnNout
Sensitivity (true positive rate)
What is SnNout
Sensitivity: true positive rate
-proportion if patients with condition who have a positive test result
-tests with high sensitivity have few false negatives, therefore a negative result rules out the condition
SnNout–> increased sensitivity and (-)result = rule out
Helpful in ruling out a diagnosis
-only helpful when you have negative result
-often used as screen tests
SpPin
Specificity
What is SpPin?
Specificity: (true negative rate)
- proportion if patients without the condition who have negative test results
- tests with high specificity have few false positives, therefore a positive result RULES IN the condition
Statistics of diagnosis
What is the Likelihood ratio?
- incorporates both sensitivity and specificity of the test and provides a direct estimate of how much a test result will change the odds I’d having a disease.
- the positive likelihood ratio tells you how much the odds if the disease increase when a test is positive (sensitivity/1-specificity)
- the negative likelihood ratio tells you how much the odds of the disease decrease when a test is negative (1-sensitivity/specificity)