International Journal of Epidemiology, Vol 28, 521-525, Copyright © 1999 by International Epidemiological Association
WC Lee
BACKGROUND: To select a proper diagnostic test, it is recommended that the
most specific test be used to confirm (rule in) a diagnosis, and the most
sensitive test be used to establish that a disease is unlikely (rule out).
These rule-in and rule-out concepts can also be characterized by the
likelihood ratio (LR). However, previous papers discussed only the case of
binary tests and assumed test results already known. METHODS: The author
proposes using the 'Kullback-Leibler distance' as a new measure of
rule-in/out potential. The Kullback- Leibler distance is an abstract
concept arising from statistics and information theory. The author shows
that it integrates in a proper way two sources of information--the
distribution of test outcomes and the LR function. The index predicts the
fate of an average subject before testing. RESULTS: Analysis of real and
hypothetical data demonstrates its applications beyond binary tests. It
works even when the conventional methods of dichotomization and ROC curve
analysis fail. CONCLUSIONS: The Kullback-Leibler distance nicely
characterizes the before-test rule-in/out potentials. It offers a new
perspective from which to evaluate a diagnostic test.
ARTICLES
Selecting diagnostic tests for ruling out or ruling in disease: the use of the Kullback-Leibler distance
Graduate Institute of Epidemiology, National Taiwan University, Taipei, ROC.
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