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.

__

FP + TN

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 + FP

__

FN + TN

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 + FP + FN