Required knowledge 171 4 - In a typical test accuracy study, a consecutive series of patients suspected of a particular condition are subjected to the index test (the test being evaluated) and then all patients receive a reference or gold standard (the best available method to establish the presence of the target condition). While in the GRADE approach appropriate accuracy studies start as high quality evidence about diagnostic accuracy, these studies are vulnerable to limitations and often lead to low quality evidence to support guideline recommendations, mostly owing to indirectness of evidence associated with diagnostic accuracy being only a surrogate for patient outcomes. - Several instruments for the evaluation of risk of bias in DTA studies are available. Cochrane Collaboration suggests a selection of the items from the QUADAS and QUADAS-2 instruments [18, 19]. Authors of systematic reviews and guideline panels can use the criteria from the QUADAS list to assess the risk of bias within and across studies. - If only diagnostic accuracy information is available, the assessment of indirectness requires additional judgments about how the correct and incorrect classification of subjects as having or not having a target condition relates to people-important outcomes.
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