Table 2.

Definitions of OMOP CDM terminology

	Definition
Standardized vocabulary	A common repository of all terminologies used within the OMOP CDM consolidated into a common format
Concept	A term defined in a medical terminology
Source values	The verbatim representation of an event record in the source data using the original codes from public code systems (e.g. ICD, National Drug Code, Current Procedural Terminology 4th edition) or locally controlled vocabularies that are not used in analysis and only provided for convenience and quality purposes
Source concepts	Source concepts represent the terms in the common healthcare terminology systems that were used in the source database, and are often found in the OMOP vocabularies as non-standard concepts
Standard concepts	Standard concepts are the respective target concepts that define the unique meaning of a clinical entity and are typically drawn from existing public terminologies such as SNOMED or created within OMOP as extension concepts if no suitable target is available
Custom concepts	Clinical terms that are custom generated for information that is not represented in the standardized vocabulary
Classification concepts	These are non-standard concepts that do not represent the data in the OMOP CDM, but instead are part of the standard concepts hierarchy, and can be used for hierarchical queries to search for a certain concept. They can be used for analysis, but they have no full equivalent ‘maps to’ links to standard concepts. Hence, classification concepts, such as MedDRA terms, require a degree of manual mapping

ICD International Classification of Disease; MedDRA Medical Dictionary for Regulatory Activities; OMOP CDM Observational Medical Outcomes Partnership common data model; SNOMED Systematized Nomenclature of Medicine Clinical Terms