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Drop the Likelihood Ratio. A Novel Non-electronic Tool for Interpreting Diagnostic Test Results
L Herich, W Lehmacher, M Hellmich1
1Prof. Dr. Martin Hellmich, Institute of Medical Statistics, Informatics and Epidemiology, University of Cologne, Kerpener Str. 62, 50924 Köln, Germany,
Objective:
To present a geometric ruler to determine predictive values of binary diagnostic test results from prevalence, sensitivity and specificity without calculation.
Methods:
On logarithmic scale the relationships between pre-/post-test odds and the likelihood ratio as well as sensitivity, specificity and the likelihood ratio appear as simple linear (additive) equations.
Results:
Each of these additive equations can be solved geometrically in form of a ruler with three scales. By amalgamation we devise a novel non-electronic tool which omits the intermediate step of likelihood ratio determination.
Conclusions:
We propose a simple geometric method to aid in interpretation of diagnostic test results for both practical and educational purposes.
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