Measurements of Test Performance

Question 1

Validity

Answer 1

The ability of the test to indicated which patients have or do not have disease. Intrinsic to the test - not affected by disease prevalence. Two metrics: sensitivity and specificity

Question 2

Sensitivity

Answer 2

The ability of a test to correctly identify those that have a disease (pick up rate). The proportion of diseased people with a positive test.

TP/ (TP+FN)

Question 3

Specificity

Answer 3

The ability of a test to correctly identify those without disease. Proportion of healthy people with a negative test.

TN/ (TN + FP)

Question 4

Positive predictive value (PPV)

Answer 4

Proportion of diseased people with a positive test. PPV is increased with higher disease prevalence.

TP/ (TP + FP)

Question 5

Negative predictive value (NPV)

Answer 5

Proportion of healthy people with a negative test. NPV is increased with lower disease prevalence.

TN/ (TN + FN)