Alchemist for HIC Hearing Health

The Alchemist Project is part of the core HIC initiatives supported by UCL/UCLH.

Cohort

The COHORT table contains records of subjects that satisfy a given set of criteria for a duration of time. The definition of the cohort is contained within the COHORT_DEFINITION table. Cohorts can be constructed of patients (Persons), Providers or Visits.

More details about cohorts in The Book of OHDSI: https://ohdsi.github.io/TheBookOfOhdsi/Cohorts.html#Cohorts

Note: the structure of this table is missing in the reference scripts https://github.com/OHDSI/CommonDataModel/tree/v5.3.1_fixes/PostgreSQL

Field Required Type FK Table Description
cohort_definition_id Yes bigint COHORT_DEFINITION A foreign key to the record containing relevant Cohort Definition information.
subject_id Yes bigint Any A foreign key to the subject in the Cohort. For e.g., records from Person, Provider, Visit Occurrence, Visit Detail, or Care Site.
cohort_start_date Yes date   The date when the Cohort Definition criteria for the Subject first match.
cohort_end_date Yes date   The date when the Cohort Definition criteria for the Subject no longer match or the Cohort membership was terminated.
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 from the combined dataset.

Conventions

  • The core of a Cohort is the unifying definition or feature of the Cohort. This is captured in the cohort_definition_id . For example, Cohorts can include patients diagnosed with a specific condition, patients exposed to a particular drug, or Providers who have performed a specific Procedure.
  • Cohort records must have a Start Date.
  • Cohort records must have an End Date, but may be set to Start Date or could have applied a censored date using the Observation Period Start Date.
  • Cohort records must contain a Subject Id, which can refer to any table. The Cohort Definition will define the type of Subject through the subject_concept_id . Common domains for Subject are the tables PERSON, PROVIDER, VISIT_OCCURRENCE, VISIT_DETAIL, and CARE_SITE.
  • A Subject can belong (or not belong) to a Cohort at any moment in time.
  • A Subject can only have one record in the COHORT table for any moment of time, i.e. it is not possible for a Person to contain multiple records indicating cohort membership that are overlapping in time.