How to Calculate Sensitivity, Specificity, Positive Predictive Value, and Negative Predictive Value

For any given test administered to a given population, it is important to calculate the sensitivity, specificity, positive predictive value, and negative predictive value, in order to determine how useful the test is to detect a disease or characteristic in the given population. If we want to use a test to test a specific characteristic in a sample population, we would like to know: How likely is the test to detect the presence of a characteristic in someone with the characteristic (sensitivity)? How likely is the test to detect the absence of a characteristic in someone without the characteristic (specificity)? How likely is someone with a positive test result to actually have the characteristic (positive predictive value)? How likely is someone with a negative test result to actually not have the characteristic (negative predictive value)? These values are very important to calculate in order to determine whether a test is useful for measuring a specific characteristic in a given population. This article will demonstrate how to calculate these values.