JAMAevidence Glossary

Terms are derived from Users' Guides to the Medical Literature: A Manual for Evidence-Based Practice, 2nd Edition and The Rational Clinical Examination: Evidence-Based Clinical Diagnosis. Updated March 2010.
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Washout period
In a crossover or N-of-1 trial, the period required for the treatment to cease to act once it has been discontinued.

Weighted kappa
A measure of the extent to which observers achieve agreement beyond the level expected to occur by chance alone. Kappa can take values from 0 (poor agreement) to 1.0 (perfect agreement).

Wild-type allele
The allele at a particular SNP that is most frequent in a population, also called “common” allele.