In short
A cohort delimits a population: patients over 65 hospitalized for sepsis in 2023. You build it from criteria combined with AND, OR and NOT, without writing SQL. Run query gives its count and attrition; Materialize freezes the membership list, which the Patient data page reads.
Defining who enters the study
This is the first concrete step in most projects, and the most consequential: inclusion criteria determine the worth of everything that follows.
In Linkr a cohort is not a list of identifiers pasted from a spreadsheet. It is a definition — a set of criteria — that can be read back, discussed, corrected and re-run. Which changes everything when you publish: you pass on the reasoning, not merely its result.
In this guide
A cohort is created from the project’s Cohorts page, then worked on in two stages that alternate until the definition holds: you set the criteria, run, read the result, correct.
Building a cohort
The builder screen, what one row stands for, the nine criterion types and their forms, combining with AND, OR and NOT, the frozen snapshot and exchange with OHDSI ATLAS.
Results, SQL and report
Running, reading the count and the attrition, reviewing the patients and the filtered tables, editing the SQL query, and producing the cohort report.
What a cohort feeds
Worth knowing, so you do not look for it where it has no effect.
A cohort filters the patient list on the Patient data page: you select the cohort, and browse only its members. The builder also has its own Patients tab, to review the members of a result without leaving the cohort — see Results, SQL and report.
A cohort does not yet filter datasets or dashboards
This is the limitation to know. To work on your cohort’s data outside the Patient data page, export the results to CSV, or take its SQL into an SQL collection.
A cohort also appears as a node in the pipeline, but that is a diagram with no execution: the node documents the chain, it filters nothing.
Cohorts at database level
A database has cohorts of its own too — the database’s Cohorts tab, outside any project. They have the same builder, without Materialize but with Derive in server mode: a new database restricted to the cohort’s members. See Derived sub-databases.
Going further
- Building a cohort — the level, the criteria, combining them, the frozen snapshot and ATLAS.
- Results, SQL and report — running, reading attrition, editing the SQL, producing the report.
- Patient data — checking that the cohort really holds the right patients.
- Derived sub-databases — drawing a new database from a cohort’s members.
- Designing a study — writing defensible inclusion criteria.