Specificity is the probability that the test will be negative among patients who do not have the disease.  A high specificity means that a positive test can rule in the disease.  A specificity of 1.0 is perfect.  Specificities greater than 0.8 are often considered very good.

Sensitivity of a test is the probability that the test is positive when given to a group of patients with the disease.  A high sensitivity means that a negative test can rule out the disease.  A sensitivity of 1.0 is perfect.  Sensitivities greater than 0.8 are often considered very good.

(For an illustration of  test effectiveness, click here )

Positive Predictive Value (PPV) of a test is the probability that the patient has the disease when restricted to those patients who test positive

Negative Predictive Value (NPV) of a test is the probability that the patient will not have the disease when restricted to all patients who test negative.

False Positive Rate of a test is the probability that the patient result is erroneously positive when a situation is normal.

False Negative Rate of a test is the probability that the patient result is erroneously negative when a situation is abnormal.