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Agreement between self-reported and observed functioning in patients with rheumatoid arthritis, osteoarthritis, and fibromyalgia, and the influence of pain and fatigue: a cross-sectional study

Objective To evaluate the relationship between self-reported and performance-based measures of functioning in rheumatoid arthritis (RA), knee osteoarthritis (OA), and fibromyalgia (FM), and the influence of pain and fatigue. Method Self-reported functioning was assessed by the Stanford Health Assessment Questionnaire, Fibromyalgia Impact Questionnaire, and Knee injury and Osteoarthritis Outcome Score. Performance-based measures of task-related physical activity included grip strength and Six-Minute Walk Test (6MWT). Assessment of Motor and Process Skills (AMPS) was used to obtain performance-based measures of activities of daily living (ADL) ability. Pain and fatigue were assessed by 100 mm visual analogue scales. Spearman’s rho correlation and regression modelling were applied. Results Correlations between self-reported functioning and performance-based measures of ADL ability were weak to moderate, and strongest in OA (r = 0.57, p = 0.002), and AMPS ADL ability measures did not enter regression models as explanatory factors for self-reported functioning. Correlations between AMPS ADL ability measures and measures of task-related physical activity were weak, except for a strong correlation between AMPS ADL motor ability and 6MWT in OA (r = 0.63, p = 0.000). The 6MWT was the only performance-based test explaining variance in AMPS motor ability (OA = 42%; FM = 11%). Pain explained variance in self-reported ability and contributed to variance in AMPS ADL motor ability measures in OA. Conclusion Self-reported and observed measures of functioning assess partly different aspects of functioning, and both approaches may therefore be relevant in a structured assessment of patients with musculoskeletal disorders.