Glossary
External Validation
Also called: independent validation
Evaluating a model on data from a different institution, population, or equipment than it was trained on.
External validation tests whether performance survives contact with a different site. It is the single most informative number in a medical AI paper and the one most frequently absent.
Where This Gets Misread
Performance drops on external validation are the norm, not the exception, and drops of ten or more points are routinely reported. A model with excellent internal and no external validation should be assumed not to generalize until shown otherwise.