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Because new diagnostic tests become available rapidly, the authors determined a need for proper assessment of tests before their implementation in clinical practice. Three factors are of pivotal importance: the selection of the proper study population, the determination of the diagnostic power including its related statistical analysis, and the relation of the new test to current diagnostic tools. Patients suspected of having a disease are those who would benefit from the application of a new test. Therefore, only those patients need be involved in the assessment study.Summary measures of diagnostic power other than sensitivity and specificity are advocated because these conventional measures depend on cutoff points and are susceptible to selection bias. The relation between the new test and existing diagnostic tools must be established to determine if the new test contributes to the diagnostic process.To avoid waste of effort and money, the authors suggest a prudent assessment approach in phases. Whereas the initial challenge consists of selection of an adequate patient population, subsequently all determinants of disease (signs, symptoms, comorbidity, and other diagnostic factors) and factors influencing the decision to use a test (patient burden and cost) are considered.