===== Measurement Domain =====

The Measurement Domain contains records of Measurements that are represented by structured values (numerical or categorical) obtained through the standardized testing or examination of a Person or Person's sample. In OMOP CDM, Measurements include the following:
  * Laboratory tests (= laboratory procedures)
  * Vital signs (= vitals)
  * Pathology reports with quantitative findings
  * Assessment instruments as staging, scales, and scores (not all of them)
  * Observable entities with the information about a quality/property to be observed (not all of them)
  * Some Clinical Findings with qualitative results of testing

The difference between a Measurement and Procedure is that a Measurement is about quantity, size, weight, distance, or capacity of a substance compared to a designated standard while a Procedure is a particular activity or process ordered by, or carried out by, a healthcare provider on the patient for a diagnostic or therapeutic purpose.

==== Overall Structure ====
Standard Concepts are taken from the following vocabularies:
^ vocabulary_id      ^ number of concepts  ^
| LOINC              | 70104               |
| SNOMED             | 13758               |
| CPT4               | 1436                |
| NAACCR             | 1414                |
| HCPCS              | 105                 |
| Nebraska Lexicon   | 19                  |
| OMOP Extension     | 18                  |
| PPI                | 8                   |
| SNOMED Veterinary  | 2                   |
| OPCS4              | 1                   |


All Standard Concepts of the Measurement Domain are intended to populate the "measurement_concept_id" field in [[https://github.com/OHDSI/CommonDataModel/wiki/MEASUREMENT/|the MEASUREMENT Standardized Clinical Data Table]]. 

==== Relationships ====
All Source Vocabularies containing Measurements are mapped to Standard Concepts through the "Maps to" relationships (with the reverse of "Mapped from"). The mapping is either provided by the source or developed by the Vocabulary Team.

==== Hierarchical crosswalks for Measurements ====
In OMOP CDM, a holistic hierarchy for Measurements is not available yet. However, there is a list of hierarchical crosswalks serving to simplify the process of concept set creation with the use of ancestry:
^ parental vocabulary_id  ^ child vocabulary_id  ^ number of hierarchical crosswalks  ^
| SNOMED                  | LOINC                | 17654                             |
| SNOMED                  | CPT4                 | 1995                              |
| SNOMED                  | HCPCS                | 42                                |
| SNOMED                  | OMOP Extension       | 20                                |
| SNOMED                  | OPCS4                | 7                                 |
| SNOMED                  | SNOMED Veterinary    | 4                                 |
| SNOMED                  | Nebraska Lexicon     | 2                                 |