an agreed minimum collection of outcomes — defined as domains and their corresponding measurement instruments — that should be measured and reported in all clinical trials, longitudinal outcome studies, or other research within a specific health condition.

COS are developed through a rigorous consensus process involving diverse stakeholders such as patient research partners, clinicians, researchers, regulators, and other decision-makers. The process typically involves:

Identifying what to measure (domains) — resulting in a Core Domain Set.

Determining how to measure these domains — selecting validated outcome measurement instruments.

By standardizing outcomes across studies, a COS improves comparability, reduces selective outcome reporting, enhances the quality of evidence synthesis, and facilitates meta-analysis.