Required knowledge 169 4 Diagnostic odds ratio Receiver operation characteristic curve (and area under the curve) - Results from individual studies should be reported with confidence intervals for each measure. - In studies of the accuracy of tests with ordinal and continuous results, positive and negative test results are defined based on a threshold for test positivity and change if the threshold is altered. This dependence on threshold is a fundamental aspect of test accuracy evaluation. - Test accuracy is not a fixed property of a test: accuracy describes the performance of a test in specific circumstances. The accuracy of a test may therefore vary with the intended use (e.g., screening versus diagnosis), population (e.g., children versus adults), setting (rural health centre in a low-income country versus urban hospital), prior tests (e.g., only signs and symptoms, or also an X-ray before CTscanning), level of training (novice versus expert readers), and many more elements. - In general, three roles can be defined for a new test relative to an existing test: (1) to select patients for whom follow-up testing may be useful (triaging); (2) to increase the accuracy of a testing strategy, by adding an extra test to the existing strategy (add-on); and (3) to replace one or more tests in the existing strategy with the (new) index test (replacement) [15] - A description of the clinical pathway should contain the following elements: (1) the setting and patient groups to be tested, including relevant prior testing; (2) the index test and any comparator index tests; (3) subsequent steps after testing, driven by the test result, such as further testing or treatment. - The purpose of testing should be specified explicitly, as well as the intended use population (asymptomatics versus symptomatics). - Details of index tests should be collected. - It is important to identify where a test is being used in a clinical pathway in each study. - The definition of the target condition and the reference standard used to identify the presence or absence of the target condition must be collected. - Collection of information about the harmful effects of testing may be desirable depending on the nature of the test. - Forest plots for diagnostic test accuracy report the number of true positives and false negatives in participants with the target condition (diseased), and true negatives and false positives in participants who do not have the target condition (non-diseased) in each study, and the estimated sensitivity and specificity, together
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