I read with interest your paper entitled "Pre and post-test probabilities and Fagan’s nomogram. I would like to add a note concerning an update on Fagan’s Nomogram. In 2011, a group of researchers published a modern version of the nomogram that they named "Bayes’ theorem nomogram"

Abushouk, Abdelrahman Ibrahim

English

PubMed

Journals Portal, Shahid Beheshti University of Medical Sciences

Emergency. 2016; 4 (3): 114-115EVIDENCE BASE MEDICINEEvolution of Fagan’s Nomogram; a CommentaryAbdelrahman Ibrahim Abushouk1∗1. Faculty of Medicine, Ain Shams University, Cairo, Egypt.Received: february 2016; Accepted: February 2016Cite this article as: Ibrahim Abushouk A.Evolution of Fagan’s Nomogram; a Commentary. Emergency. 2016; NN(I):114-115.Dear EditorI read with interest your paper entitled “Pre and post-testprobabilities and Fagan’s nomogram” (1). I would like to adda note concerning an update on Fagan’s Nomogram. Gener-ally, the basic idea of most nomograms is having the scalesof 3 variables in a manner that if you draw a straight line be-tween 2 values, the 3rd value is found where the line inter-sects the 3rd scale (2). They were initially developed in the1980s by Maurice D’Ocange. Nomograms remained popu-lar in medical practice until the invention of pocket calcula-tors and computers. Their use increased again with the in-troduction of evidence-based medicine in clinical practice.In a letter to the New England Journal of Medicine in July1975, Dr Terry Fagan displayed a test characterization toolthat went on to carry his name as the Fagan’s nomogram (3).This nomogram is a simple application of the Bayes’ theo-rem, which establishes a rule to calculate the post-test prob-ability of a disease. However, Fagan’s nomogram had a setof drawbacks that limited its use in clinical practice. Thesedrawbacks included: 1- The original Bayes’ theorem is de-signed to deal with odds ratios, not probabilities, so alge-braic conversion is needed to calculate probability. 2- Mostdiagnostic tests are characterized in terms of sensitivity &specificity in the literature, which need special equations tobe converted into likelihood ratios (4). Noticing these diffi-culties, in 2011, a group of researchers published a modernversion of the nomogram that they named “Bayes’ theoremnomogram”. The new nomogram targeted the former prob-lems using: A- Parallel lines for probability and odds on eachside of the nomogram figure. B- The inner lip along the en-tire circle contains values for sensitivity and specificity thatcan be connected to calculate the likelihood ratio of a cer-tain diagnostic test (5). As illustrated in figure (A), a pretestprobability of 18% and a likelihood ratio (LR+) of 2.8 for a di-agnostic test would give a posttest probability of 38%. Fur-ther advantages of the modern nomogram include: - In Rare∗Corresponding Author: Abdelrahman Ibrahim Abushouk; Ain Shams Uni-versity, Cairo, Egypt. E-mail: abdelrahman.abushouk@med.asu.edu.eg .Figure 1: The modern Bayes’ theorem nomogram with an exampleof probability calculation as shown by the green line.disorders, having a very low pretest probability implies per-forming a diagnostic test with a fairly high LR (+). In Fa-gan’s nomogram, the high values of LR are compressed in atight portion over that scale (4), while in this model; a morespaced representation of high LR is feasible. - Replacing thelinear form with a circular one works better for complex di-agnostic protocols where addition of multiple arrows for dif-ferent diagnostic tests may be required (5). Considering thementioned superiorities of the Bayes’ theorem nomogramover the conventional Fagan’s nomogram, it is highly recom-mended for clinicians to use it in conducting diagnostic pro-tocols and formulating therapeutic plans.References1. Safari S, Baratloo A, Elfil M, Negida A. Part 4: Pre and PostTest Probabilities and Fagan’s Nomogram. EMERGENCY-An Academic Emergency Medicine Journal. 2016;4.2. Thimbleby H, Williams D, editors. Using nomograms toreduce harm from clinical calculations. Healthcare Infor-This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0).Downloaded from: www.jemerg.com115 Emergency. 2016; 4 (3): 114-115matics (ICHI), 2013 IEEE International Conference on;2013: IEEE.3. Fagan TJ. Letter: nomogram for Bayes theorem. The NewEngland journal of medicine. 1975;293(5):257-.4. Miettinen OS, Caro JJ. Foundations of medical diagnosis:what actually are the parameters involved in Bayes’ theo-rem? Statistics in medicine. 1994;13(3):201-9.5. Marasco J, Doerfler R, Roschier L. Doc, what are mychances. UMAP Journal. 2011;32:279-98.This open-access article distributed under the terms of the Creative Commons Attribution NonCommercial 3.0 License (CC BY-NC 3.0).Downloaded from: www.jemerg.com

Evolution of Fagan's Nomogram; a Commentary

Abstract

Similar works

Full text

Available Versions

Journals Portal, Shahid Beheshti University of Medical Sciences

Directory of Open Access Journals