Glossary

What is Semantic drift?

Updated September 1, 2026

Semantic drift is the same field coming to mean something different over time. A lab changes its assay method, a diagnosis is recoded under a new guideline, a wearable updates the algorithm behind a metric, and the values keep flowing under the old name with a new meaning.

Because the schema is unchanged, quality checks pass. The Data Trust Index catches semantic drift through Concordance, corroboration across independent sources (does the lab result still agree with the wearable, does the EHR still match the claim), and through Validation, the clinical linkage of a data type to outcomes and peer-reviewed evidence. When a field stops corroborating and its clinical meaning is no longer established, its score falls.

This is the failure that makes clean data dangerous: the record is complete, well formed, and wrong in a way no format check can see.