In practice, the outcomes of diagnostic tests are mostly interpreted and operationalized as binary—that is, as positive or negative—for the presence of a target condition. However, the actual outcome of a test is rarely a binary one. For example, the results of laboratory tests are typically measured on continuous scales, and the same applies to measures summarizing scans with modern imaging modalities, such as the standardized uptake value in positron emission tomography. When test results are measured on an explicitly defined and observed scale as in these examples, a binary outcome is defined on the basis of an explicit threshold for test positivity. When tests involve interpretation by a human observer, a similar model with a threshold for test positivity has been used widely. However, ...