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Keywords
- Common metric; DASH; Disability and Health; HAQ; International Classification of Functioning; Multidimensional HAQ; PROMIS-SF; Rasch measurement model; Scale banking; WHODAS 2.0; WOMAC. (1)
- FIM; Functional Independence Measure; HAQ; Health Assessment Questionnaire; WHODAS 2.0; World Health Organization Disability Assessment Schedule; outcome assessment; rheumatoid arthritis; stroke; psychometrics. (1)
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.
Keywords: Common metric; DASH; Disability and Health; HAQ; International Classification of Functioning; Multidimensional HAQ; PROMIS-SF; Rasch measurement model; Scale banking; WHODAS 2.0; WOMAC.
Abstract
Objectives: To develop a common reference metric of functioning, incorporating generic and health condition-specific disability instruments, and to test whether this reference metric is invariant across 2 health conditions.
Design: Psychometric study using secondary data analysis. Firstly, the International Classification of Functioning, Disability and Health (ICF) Linking Rules were used to examine the concept equivalence between the World Health Organization Disability Assessment Schedule (WHODAS 2.0), Health Assessment Questionnaire (HAQ), and Functional Independence Measure (FIMTM). Secondly, a scale-bank was developed using a reference metric approach to test-equating, based on the Rasch measurement model.
Participants: Secondary analysis was performed on data from 487 people; 61.4% with rheumatoid arthritis and 38.6% with stroke.
Results: Three sub-domains of the WHODAS 2.0 and all items of the HAQ and FIMTM motor mapped on to the ICF chapters d4 Mobility, d5 Self-care and d6 Domestic life. Test-equating of these scales resulted in good model fit, indicating that a scale bank and associated reference metric across these 3 instruments could be created.
Conclusion: This study provides a transformation table to enable direct comparisons among instruments measuring physical functioning commonly used in rheumatoid arthritis (HAQ) and stroke (FIMTM motor scale), as well as in people with disability in general (WHODAS 2.0).
Keywords: FIM; Functional Independence Measure; HAQ; Health Assessment Questionnaire; WHODAS 2.0; World Health Organization Disability Assessment Schedule; outcome assessment; rheumatoid arthritis; stroke; psychometrics.