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Type: Journal article
Title: The two-step Fagan's nomogram: ad hoc interpretation of a diagnostic test result without calculation
Author: Caraguel, C.
Vanderstichel, R.
Citation: Evidence - Based Medicine, 2013; 18(4):125-128
Publisher: BMJ Group
Issue Date: 2013
ISSN: 1356-5524
Statement of
Charles G B Caraguel, Raphaël Vanderstichel
Abstract: In 1975, Fagan published a nomogram to help practitioners determine, without the use of a calculator or computer, the probability of a patient truly having a condition of interest given a particular test result. Nomograms are very useful for bedside interpretations of test results, as no test is perfect. However, the practicality of Fagan's nomogram is limited by its use of the likelihood ratio (LR), a parameter not commonly reported in the evaluation studies of diagnostic tests. The LR reflects the direction and strength of evidence provided by a test result and can be computed from the conventional diagnostic sensitivity (DSe) and specificity (DSp) of the test. This initial computation is absent in Fagan's nomogram, making it impractical for routine use. We have seamlessly integrated the initial step to compute the LR and the resulting two-step nomogram allows the user to quickly interpret the outcome of a test. With the addition of the DSe and DSp, the nomogram, for the purposes of interpreting a dichotomous test result, is now complete. This tool is more accessible and flexible than the original, which will facilitate its use in routine evidence-based practice. The nomogram can be downloaded at:
Keywords: Humans; Clinical Laboratory Techniques; Nomograms; Probability; Bayes Theorem; Sensitivity and Specificity
Rights: © 2013 the BMJ Publishing Group Ltd.
RMID: 0020131982
DOI: 10.1136/eb-2013-101243
Appears in Collections:Animal and Veterinary Sciences publications

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