title: Drop the Likelihood Ratio. A Novel Non-electronic Tool for Interpreting Diagnostic Test Results.
abstract: 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.
authors.forename: L
authors.initials: L
authors.lastname: Herich
authors.forename: W
authors.initials: W
authors.lastname: Lehmacher
authors.affiliation: Prof. Dr. Martin Hellmich, Institute of Medical Statistics, Informatics and Epidemiology, University of Cologne, Kerpener Str. 62, 50924 Köln, Germany, E-mail: martin.hellmich@uni-koeln.de.
authors.forename: M
authors.initials: M
authors.lastname: Hellmich
mesh_terms: D001499:Bayes Theorem; D003627:Data Interpretation, Statistical; D003661:Decision Support Techniques; D016013:Likelihood Functions; D016015:Logistic Models; D011237:Predictive Value of Tests
keywords: Bayes’ rule; Caraguel-Vanderstichel nomogram; diagnostic test; ruler