Rates of change in a large clinical terminology: three years experience with SNOMED Clinical Terms

The Systematized Nomenclature of Medicine, Clinical Terms (SNOMED CT) was produced by merging SNOMED Reference Terminology (RT) with Clinical Terms version 3 (CTV3). It was first released in January 2002. This paper summarizes the overall size of the terminology and its rates of change over a period of three calendar years, comprising six subsequent releases each occurring at six month intervals. Rates of change in raw table size are reported for the concepts, descriptions, and relationships tables. Other measures of change are the number of identifiers made inactive and the reasons for this, as well as the number and rate of changes in the subsumption hierarchies and defining relationships. Awareness of the rate of change in the terminology can help terminology developers focus attention on needed infrastructure support and capacity for handling updates and refinements, and can help application developers by highlighting the need for managing terminology change in applications.