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A note on Youden's J and its cost ratio
1Department of Clinical Psychology, Faculty of Psychology and Education, Vrije Universiteit, Van der Boechorststraat 1, 1081 BT Amsterdam, the Netherlands. n.smits@psy.vu.nl
BMC Medical Research Methodology
|October 6, 2010
Summary
The Youden index, used for medical test thresholds, is not truly optimal as its cost ratio changes with disease prevalence. Researchers should use a decision theoretic framework with specific cost ratios for accurate threshold selection.
Area of Science:
- Medical Diagnostics
- Biostatistics
- Decision Theory
Background:
- The Youden index, calculated as sensitivity + specificity - 1, is commonly used to determine optimal thresholds for medical diagnostic tests.
- This index implicitly applies decision theory principles to threshold selection.
Purpose of the Study:
- To evaluate the optimality of the Youden index for setting thresholds in medical tests.
- To investigate the influence of disease prevalence on the Youden index's performance.
Main Methods:
- The study analyzes the decision-theoretic underpinnings of the Youden index.
- It examines how the implicit cost ratio of the Youden index relates to disease prevalence.
Main Results:
- The Youden index's implicit cost ratio is directly linked to the disease prevalence (1 - prevalence).
- A threshold optimized using the Youden index is only optimal for a specific prevalence and its associated cost ratio.
Conclusions:
- The Youden index is not a universally optimal decision rule due to its prevalence-dependent cost ratio.
- Researchers are advised to define and utilize their specific cost ratios within a decision-theoretic framework for genuinely optimal threshold determination.
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