Functioning is an essential outcome for rheumatoid arthritis (RA) management. This study aimed to standardize the reporting of such PROMs measuring functioning in RA to facilitate comparability.

The Common Item Non‐Equivalent Groups Design (NEAT) with the Health Assessment Questionnaire (HAQ) was used as a standard scale across data sets from various countries (incl. UK, Turkey, and Germany) to establish a standard metric. Other PROMs included are the Physical Function items of the Multidimensional Health Assessment Questionnaire (MDHAQ), Disabilities of Arm, Shoulder and Hand (DASH), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), World Health Organization Disability Assessment Schedule Version 2.0 (WHODAS 2.0), and four short forms (20, 10, 6, and 4 physical function items) from the Patient‐Reported Outcomes Measurement Information System (PROMIS). PROMs were described using Standard Error of Measurement (SEM) and Smallest Detectable Difference (SDD). The Rasch Measurement model was used to create the standard metric. The range of SEM is 0.2 (MDHAQ) to 7.4 (SF36‐PF). SDD revealed a range from 9.7 % (WOMAC‐RAT) to 33.5 % (WHODAS‐PF).

In conclusion, the scores between the Daily Activity PROMs commonly used in RA can now be compared. Factors such as SEM and SDD help determine the choice of PROM in clinical practice and research.