Observation

The Observation table captures clinical facts about a Person obtained in the context of examination, questioning or a procedure. Any data that cannot be represented by any other domains, such as social and lifestyle facts, medical history, family history, etc. are recorded here.

Observations are like measurements - but where the values cannot be fit into either numeric results or coded values.

Field	Required	Type	FK Table	Description
observation_id	Yes	bigint		A unique identifier for each Observation.
person_id	Yes	bigint	PERSON	A foreign key identifier to the Person about whom the Observation was recorded. The demographic details of that Person are stored in the PERSON table.
observation_concept_id	Yes	bigint	CONCEPT	A foreign key to the standard Observation Concept identifier in the Standardized Vocabularies.
observation_date	Yes	date		The UTC date of the Observation.
observation_datetime	No	datetime		The date and time of the Observation.
observation_type_concept_id	Yes	bigint	CONCEPT	A foreign key to the predefined Concept identifier in the Standardized Vocabularies reflecting the type of the Observation. Can be used to determine the provenance of the record, from the OHDSI list of Accepted Concepts.
value_as_number	No	numeric/float		The Observation result stored as a number. This is applicable to Observations where the result is expressed as a numeric value.
value_as_string	No	varchar(50)		The Observation result stored as a string. This is applicable to Observations where the result is expressed as verbatim text.
value_as_concept_id	No	bigint	CONCEPT	A foreign key to an Observation result stored as a Concept ID. This is applicable to Observations where the result can be expressed as a Standard Concept from the Standardized Vocabularies (e.g., positive/negative, present/absent, low/high, etc.).
qualifier_concept_id	No	bigint	CONCEPT	A foreign key to a Standard Concept ID for a qualifier (e.g., severity of drug-drug interaction alert).
unit_concept_id	No	bigint	CONCEPT	A foreign key to a Standard Concept ID of measurement units in the Standardized Vocabularies.
provider_id	No	bigint	PROVIDER	A foreign key to the provider who was responsible for making the Observation.
visit_occurrence_id	No	bigint	VISIT_OCCURRENCE	A foreign key to the Visit Occurrence during which the Observation was recorded.
visit_detail_id	No	bigint	VISIT_DETAIL	A foreign key to the Visit Detail during which the Observation was recorded.
observation_source_value	No	varchar(50)		The Observation code as it appears in the source data. This code is mapped to a standard Concept in the Standardized Vocabularies (column observation_source_concept_id ), and the original code from the source EHR is stored here for reference.
observation_source_concept_id	No	bigint	CONCEPT	A foreign key to a Concept that refers to the code used in the source.
unit_source_value	No	varchar(50)		The source code for the unit as it appears in the source data. This code is mapped to a standard Unit Concept in the Standardized Vocabularies (column unit_concept_id ), and the original code from the source EHR is stored here for reference.
qualifier_source_value	No	varchar(50)		The source value associated with a qualifier to characterize the Observation.
last_updated_datetime	Yes	datetime		Initially this is the time the row was written to OMOP. If the row is subsequently updated, it then becomes the most recent update time.
deleted_datetime	No	datetime		NULL initially. Set to the time when the row was marked for deletion. A value in this column sent to the central data source will result in this row being deleted (by person_id ) from the combined dataset. Deletions only need to be sent once.

Conventions

• Observations differ from Measurements in that they do not require a standardized test, or some other activity, to generate clinical fact. Typical Observations are medical history, family history, the stated need for certain treatment, social circumstances, lifestyle choices, healthcare utilization patterns, etc.
• If the generation of clinical facts requires a standardized testing such as lab testing or imaging, and leads to a standardized result, the data item is recorded in the MEASUREMENT table.
• If the clinical fact observed determines a sign, symptom, diagnosis of a disease or other medical condition, it is recorded in the CONDITION_OCCURRENCE table.
• Valid Observation Concepts are not enforced to be from any domain. They still should be Standard Concepts, and they typically belong to the “Observation” or sometimes “Measurement” domain.
• Observations can be stored as attribute-value pairs, with the attribute as the Observation Concept and the value representing the clinical fact. This fact can be a Concept (stored in value_as_concept ), a numerical value (value_as_number ), or a verbatim string (value_as_string ). Even though Observations do not have an explicit result, the clinical fact can be stated separately from the type of Observation in the value_as_ fields.
• The type of Observation in observation_type_concept_id can be used to determine the provenance of the Observation record, as in whether the measurement was from an EHR system, registry, or other sources. OHDSI povides a list of Accepted Concepts.
• It is recommended for Observations that are suggestive statements of positive assertions to have a value of 4188539|Yes recorded, even though the NULL value is equivalent.
• Valid Concepts of the value_as_concept field are not enforced, but typically belong to the “Meas Value” domain.
• For numerical facts a Unit can be provided in the unit_concept_id .
• For facts represented as Concepts no domain membership is enforced.
• Note that the value of value_as_concept_id may be provided through mapping from a source Concept which contains the content of the Observation. In those situations, the CONCEPT_RELATIONSHIP table in addition to the “Maps to” record contains a second record with the relationship_id set to “Maps to value”. For example, the ICD9CM V17.5 concept 44828510|Family history of asthma has a “Maps to” relationship to 4167217|Family history of clinical finding , as well as a “Maps to value” record to 317009|Asthma .
• The qualifier_concept_id field contains all attributes specifying the clinical fact further, such as degrees, severities, drug-drug interaction alerts, etc.
• The Visit during which the Observation was made is recorded through a reference to the VISIT_OCCURRENCE table. This information is not always available.
• The Provider making the Observation is recorded through a reference to the PROVIDER table. This information is not always available.