Methods Inf Med 2015; 54(03): 283-287
DOI: 10.3414/ME14-01-0091
Original Articles
Schattauer GmbH

Drop the Likelihood Ratio

A Novel Non-electronic Tool for Interpreting Diagnostic Test Results
L. Herich
1   Institute of Medical Statistics, Informatics and Epidemiology, University of Cologne, Cologne, Germany
,
W. Lehmacher
1   Institute of Medical Statistics, Informatics and Epidemiology, University of Cologne, Cologne, Germany
,
M. Hellmich
1   Institute of Medical Statistics, Informatics and Epidemiology, University of Cologne, Cologne, Germany
› Author Affiliations
Further Information

Publication History

received: 09 September 2014

accepted: 05 January 2014

Publication Date:
22 January 2018 (online)

Summary

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.