15 General introduction and outline of this thesis 1 disease is indispensable for clinical utility [30, 31]. Utility of the diagnostic test is evaluated in the later stages, starting with the more subjective ‘diagnostic thinking efficacy’ (level 3), that is, how do physicians appreciate the information of the diagnostic test, and ‘therapeutic efficacy’ (level 4), that is, do physicians think that the diagnostic test changed their decision-making and planned patient management [30, 32]. These two phases are criticized for their subjectivity and lack of validity, as intended behaviour may not reflect actual behaviour [30]. In the Fryback-Thornbury hierarchy, clinical utility is considered level 5, ‘Patient outcome efficacy’. This may include the rate of accurately prevented unbeneficial diagnostic thyroid surgeries for benign thyroid nodules as well as changes in health-related quality of life (HRQoL) [30-32]. Clinical utility is best evaluated using a randomized study design [30]. The final level 6 is ‘Societal efficacy’ and includes the assessment of the use of resources and medical benefits on a societal level as opposed to the patients’ individual risks and benefits. This includes cost-effectiveness analyses, in which utility is most often defined as the number of quality-adjusted life years (QALYs) gained [30-32]. Figure 1. The Fryback-Thornbury hierarchy. The diagnostic randomized controlled trial Diagnostic randomized controlled trials (RCTs) are defined as randomized comparisons of two diagnostic interventions (i.e., experimental versus standard) that measure the impact of the experimental diagnostic intervention on health outcomes as compared to the standard diagnostic intervention [33, 34]. Whereas cohort studies provide the relative diagnostic accuracy of an additional test as compared to the reference standard, diagnostic RCTs may additionally inform on the clinically important consequences of that diagnostic accuracy [33].
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