Measuring facts about disability may not reflect their personal impact. An individualized values instrument has been used to weight difficulty in performing activities of daily living in rheumatoid arthritis, and calculate personal impact (Personal Impact Health Assessment Questionnaire; PI HAQ). This study aimed to evaluate the PI HAQ in osteoarthritis (OA).
Study 1: 51 people with OA completed short and long versions of the value instrument at 0 and 1 week. Study 2: 116 people with OA completed the short value instrument, disability and psychological measures at 0 and 4 weeks.
Study 1: The eight-category and 20-item value instruments correlated well (r = 0.85) and scores differed by just 2.7%. The eight-category instrument showed good internal consistency reliability (Cronbach's alpha = 0.85) and moderate one-week test-retest reliability (r = 0.68, Wilcoxon signed-rank test p = 0.16, intra-class correlation coefficient [ICC] 0.62). Study 2: Values for disability were not associated with disability severity or clinical status. After weighting disability by value, the resulting PI HAQ scores were significantly associated with dissatisfaction with disability, perceived increase in disability, poor clinical status and life dissatisfaction, and differed significantly between people with high and low clinical status (convergent and discriminant construct validity). There was moderate association with the disease repercussion profile disability subscale (r = 0.511; p < 0.001) (criterion validity). The PI HAQ was stable over four weeks (ICC 0.81).
These studies provide an initial evaluation of an instrument to measure the personal impact of disability in people with OA, setting disability within a personal context. Further studies, including sensitivity to change, are required.