# Sensitivity and Specificity of diagnostic tests

 Sensitivity The probability of the test finding disease among those who have the disease or the proportion of people with disease who have a positive test result. Sensitivity = true positives / (true positives + false negatives) Specificity The probability of the test finding NO disease among those who do NOT have the disease or the proportion of people free of a disease who have a negative test. Specificity = true negatives / (true negatives + false positives) Positive Predictive Value (PPV) The percentage of people with a positive test result who actually have the disease. Positive predictive value = true positives / (true positives + false positives) Negative Predictive Value (NPV) The percentage of people with a negative test who do NOT have the disease. Negative predictive value = true negatives / (true negatives + false negatives) Likelihood Ratio Positive (LR+) The odds that a positive test result would be found in a patient with, versus without, a disease. Likelihood Ratio Positive (LR+) = Sensitivity / (1 - Specificity). Likelihood Ratio Negative (LR-) The odds that a negative test result would be found in a patient without, versus with, a disease. Likelihood Ratio Negative (LR-) = (1- Sensitivity) / Specificity. Go back to this tool