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Prodinger, Birgit; Coenen, Michaela; Hammond, Alison; Küçükdeveci, Ayşe A.; Tennant, Emeritus Alan (2020): Scale‐Banking for Patient Reported Outcome Measures (PROMs) Measuring Functioning in Rheumatoid Arthritis: A Daily Activities Metric. In: Arthritis Care & Research [Forthcoming]
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Abstract

Objective Functioning is an important outcome for rheumatoid arthritis (RA) management. Heterogeneity of respective patient‐reported outcome measures (PROMs) challenges direct comparisons between their results. This study aimed to standardize reporting of such PROMs measuring functioning in RA to facilitate comparability. Methods Common Item Non‐Equivalent Groups Design (NEAT) with the Health Assessment Questionnaire (HAQ) as a common scale across data sets from various countries (incl. UK, Turkey and Germany) to establish a common 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). As the HAQ includes mobility, self‐care and domestic life items, this study focuses on these three domains. PROMs were described using Standard Error of Measurement (SEM) and Smallest Detectable Difference (SDD). Rasch Measurement model was used to create the common metric. Results 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). PROMs co‐calibration revealed fit to the Rasch measurement model. A transformation table was developed to allow exchange between PROMs scores. Discussion Scores between the Daily Activity PROMs commonly used in RA can now be compared. Factors such as SEM and SDD help determine choice of PROM in clinical practice and research.