a comprehensive guidance resource developed by the Outcome Measures in Rheumatology (OMERACT) initiative. It outlines the standards, principles, and step-by-step methods for developing, evaluating, and endorsing Core Outcome Sets (COS) for use in clinical trials and other health research. The Handbook serves as a reference point for researchers, clinicians, and patient partners to ensure consistency, transparency, and rigor in outcome measurement across rheumatology and musculoskeletal studies.