A parable in four visits. A parable THE ARCHITECTURE OF MEDICAL TEST EVALUATIONS. παραβολή

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1 Biomarker & Test Evaluation Program Predisposition Risk Stratification Early Detection Surveillance Disease THE ARCHITECTURE OF MEDICAL TEST EVALUATIONS Diagnosis Monitoring (Disease) Staging Treatment Selection Prognosis Monitoring (Treatment ) Patrick MM Bossuyt A parable in four visits παραβολή the name given by Greek rhetoricians to any fictive illustration in the form of a brief narrative A parable Visit 1 Wikipedia careerrenovators.com 1

2 Pulmonary Embolism Artificial Nose 1.bp.blogspot.com Artificial Nose Artificial Nose PE-Sensor Yuri Arcurs Photography 2

3 A parable Visit 2 Artificial Nose PE-Sensor Lots of data Certificate CE mark Directive 98/79/EC Declaration of conformity Four risk categories: Annex II List A (HIV I and II, Hepatitis B, C and D, Annex II List B (rubella, toxoplasmosis and phenylketonuria) IVDs for self-testing Other IVD 3

4 Evidence-based medicine A parable Visit 3 Artificial Nose PE-Sensor Diagnostic Accuracy Study Series of Patients BioMarker Reference standard Cross-classification Diagnostic Accuracy Study The results 2,302 ED Patients Reference Standard PE-sensor Target Other Multislice CT Cross-classification Positive Negative 4

5 The results Reference Standard Target Other Positive TP FP Negative FN TN knol.google.com Jaapa.com Test Strategy Test Strategy 5

6 Test Strategy Test Strategy A parable Visit 4? Evaluation Medical Tests Three questions Question Feature 1. Technical Performance Is it true? Technical Performance Is it meaningful? Clinical Performance Is it useful? Clinical Effectiveness 6

7 Diagnostic Accuracy 2. Clinical Performance BioMarker Gold Standard 7

8 Diagnostic Accuracy Study 2,302 ED Patients Simplify D-dimer Multislice CT Cross-classification The results The results Reference Standard Reference Standard Target Other Target Other Positive TP FP Positive Negative FN TN Negative 21 1,591 Measures of Diagnostic Test Accuracy Sensitivity & Specificity 81 % 73 % Predicted Values 13 % 99 % Likelihood Ratios Diagnostic Odds Ratio Clinical Effectiveness PE Non PE Positive Negative 21 1,591 8

9 Clinical Effectiveness Consequences of Testing Explanation Health Outcome Health outcomes that matter to patients and society: to prevent premature death, to restore or maintain functional health. Probabilistic Not all outcomes will be observed in everyone tested; evaluations will be made at the group level, and expressed in terms of a distribution of outcomes. Comparative Clinical utility from a testing or marker based strategy is defined relative to a comparator strategy: current best standard practice. Randomized Clinical Trial Medical Test RCT 9

10 Medical Test Result How Tests Affect Outcome Clinical Response Intervene Do not Intervene Patient Outcome Medical Test Result Emotional Social Cognition Clinical Response Behavior Intervene Do not Intervene Clinical Outcome P.M. Bossuyt and K. McCaffery, MDM, 2009 Roles of tests Roles of Medical Tests In Clinical Pathway 10

11 Clinical Dx Accuracy Target..not just disease How good is the test in correctly classifying patients as being diseased? Clinical Dx Accuracy How good is the test in correctly classifying patients as having the target condition? 11

12 Value of Medical Tests Two views on medical tests Essentialist Consequentialist Essentialism Consequentialism the theory that the value of a marker or a medical test should be judged by the trueness of its results the theory that the value of a marker or a medical test should be judged by the value of its consequences 12

13 Two views on tests Two views on tests Essentialism Consequentialism Essentialism Consequentialism Key Value Key Value Truth Usefulness Focus Focus Results Consequences Emphasis Emphasis Validity Utility Statistics Statistics Accuracy Health Outcomes Artificial Nose PE-Sensor A parable Coda Artificial Nose SensorFreshQ SensorFreshQ 13

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