Predictive Value Theory

The diagnostic value of a procedure is defined by its sensitivity, specificity, predictive value and efficiency. The formula are summarized below.

 Test Positive Test Negative Disease Present True Positive (TP) False Negative (FN) Disease Absent False Positive (FP) True Negative (TN)

SENSITIVITY:

Sensitivity of a test is the percentage of all patients with disease present who have a positive test.

__TP___ X 100 = Sensitivity (%)
TP + FN

SPECIFICITY:

Specificity of a test is the percentage of all patients without disease who have a negative test.

__TN___ X 100 = Specificity (%)
FP + TN

PREDICTIVE VALUE:

The predictive value of a test is a measure (%) of the times that the value (positive or negative) is the true value, i.e. the percent of all positive tests that are true positives is the Positive Predictive Value.

__TP___ X 100 = Predictive Value of a Positive Result (%)
TP + FP

__TN___ X 100 = Predictive Value Negative Result (%)
FN + TN

TEST EFFICIENCY:

The efficiency of a test is the percentage of the times that the test give the correct answer compared to the total number of tests.

____TP + TN______ X 100 = Efficiency of a Test Result (%)
TP + TN + FP + FN