Diagnostic Studies Made Easy

Diagnostic studies have two components: the test result (predictor) and the disease status (outcome). Test sensitivity is the percentage of the true positive results in those having the disease, while test specificity is the percentage of the true negative results in those patients who do not have the disease. The predictive value of a positive test is the probability that a patient with a positive result has the disease, while the predictive value of a negative test is the probability of a patient with a negative result not having the disease. The likelihood ratio is the likelihood that a patient having the disease would have a certain result divided by the likelihood that a patient without the disease would have the same result. Receiver operating characteristics (ROC) curves illustrate the diagnostic characteristics of a test having an ordinal or continuous result.