The reliability and validity of the English version of the Evaluation of Daily Activity Questionnaire for people with rheumatoid arthritis
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Objectives. The Evaluation of Daily Activity Questionnaire (EDAQ) includes 138 items in 14 domains
identified as important by people with RA. The aim of this study was to test the validity and reliability
of the English EDAQ.
Methods. A total of 502 participants completed two questionnaires 3 weeks apart. The first consisted of
the EDAQ, HAQ, RA Quality of Life (RAQoL) and the Medical Outcomes Scale (MOS) 36-item Short-Form
Health Survey (SF-36v2), and the second consisted of the EDAQ only. The 14 EDAQ domains were tested
for: unidimensionality—using confirmatory factor analysis; fit, response dependency, invariance across
groups (differential item functioning)—using Rasch analysis; internal consistency [Person Separation
Index (PSI)]; concurrent validity—by correlations with the HAQ, SF-36v2 and RAQoL; and testretest
reliability (Spearman’s correlations).
Results. Confirmatory factor analysis of the 14 EDAQ domains indicated unidimensionality, after adjustment
for local dependency in each domain. All domains achieved a root mean square error of approximation
<0.10 and satisfied Rasch model expectations for local dependency. DIF by age, gender and
employment status was largely absent. The PSI was consistent with individual use (PSI = 0.94 for all
14 domains). For all domains, except Caring, concurrent validity was good: HAQ (rs = 0.720.91),
RAQoL (rs = 0.670.82) and SF36v2 Physical Function scale (rs =0.60 to 0.84) and testretest reliability
was good (rs = 0.700.89).
Conclusion. Analysis supported a 14-domain, two-component structure (Self care and Mobility) of the
EDAQ, where each domain, and both components, satisfied Rasch model requirements, and have robust
reliability and validity.