Screening Test Statistics (Sensivity, PPV etc) Flashcards
Positive Test
Disease Present
True Positive
Positive Test
Disease Absent
False Positive
Negative Test
Disease Present
False Negative
Negative Test
Disease Absent
True Negative
What is Sensitivity and what is the formula for it?
Sensitivity = TP/(TP+FN)
The proportion of patients with the condition who have a positive test
What is the difference between PPV and NPV?
Positive predictive value
Negative predictive value
PPV = TP/ (TP + FP)
The chance that the patient has the condition if the diagnostic test is positive.
NPV = TN/(TN + FN)
The chance that the patient does not have the condition if the diagnostic test is negative.
What is a precise test (precision)?
A test that is able to produce the same measurements with repeated tests.
What is specificity and what is the formula for it?
Specificity = TN/ (TN+FP)
The proportion of patients without the condition who have a negative test result.
Describe positive predictive and give the formula for it.
PPV = TP / (TP + FP)
The chance that the patient has the condition if the diagnostic test is positive
What is negative predictive value?
Give the formula for it.
NPV = TN / (TN + FN)
The chance that the patient does not have the condition if the diagnostic test is negative
What is the likelihood ratio for a positive test result.
Give its formula.
LR+ =sensitivity / (1 - specificity)
How much the odds of the disease increase when a test is positive
What is the likelihood ratio for a negative test result?
Give the formula for it.
How much the odds of the disease decrease when a test is negative
LR- = (1 - sensitivity) / specificity
