Evidence-appraisal glossary
Fagan nomogram
A graphical tool for turning a pre-test probability into a post-test probability: you draw a straight line from the pre-test probability through the test's likelihood ratio to read off the result.
Also called: Fagan's nomogram.
The Fagan nomogram is a visual shortcut for Bayes' theorem, sparing the reader from converting probabilities to odds by hand. It has three vertical scales, pre-test probability on the left, likelihood ratio in the middle, and post-test probability on the right, and a ruler laid across the first two points crosses the third at the answer. It is a convenience for reading a single result, not a separate statistical method, and its accuracy is limited by how precisely you can place the line.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.