Diagnostic tests are important aspects in making a diagnosis. Certain statistical information about the accuracy and validity of the tests themselves can help turn the data into usable, applicable information. Some of the most important epidemiological values of diagnostic tests include sensitivity and specificity, false positives and false negatives, positive and negative predictive values, likelihood ratios, and pre-test and post-test probabilities. For example, a test with high sensitivity is useful as a screening test, whereas high specificity is required for an accurate diagnosis. Alternatively, positive and negative predictive values help determine the probability of disease in the case of certain test results.