Sensitivity, Specificity, PPV, NPV

Sensitivity is TRUE POSITIVE RATE.

2x2 table 

Sensitive test picks all diseased and also sometimes without disease. That means it won’t miss the disease.

Sensitivity is a measure of  test positive out of total diseased. 

Specificity is TRUE NEGATIVE RATE.

Specific test picks only the diseased one but may sometime miss the disease itself.

Sensitivity and specificity are not dependent upon the disease prevalence rate.

Specificity is measure of true negative out of total healthy patient. 

Predictive values depend upon the prevalence of disease and accuracy of the test.

Positive Predictive Value is the proportion of the people with positive test who actually have disease.

Negative Predictive Value is the proportion of the people with negative test who actually do not have disease.

	PPV	NPV
Definition	% that a person with positive test is actually diseased.	% change that a person with negative test is actually disease free.
Use	Proceed with a patient with positive test	Proceed with a patient with negative test
Relation to prevalence	Low prevalence low PPV High prevalence high PPV	High prevalence low NPV Low prevalence High NPV