Evaluation of a modified arthritis self-efficacy scale for an ankylosing spondylitis UK population.

OBJECTIVES To evaluate an Ankylosing Spondylitis-specific Arthritis Self-Efficacy Scale (ASES-AS) United Kingdom (UK) secondary care population. METHODS The ASES-AS is based on the 8-item ASES with minor alterations in phraseology. Patients from ten secondary care rheumatology centres across England were asked to complete a postal questionnaire concerning sociodemographic and clinical characteristics: Bath AS Functional Index (BASFI), Bath AS Disease Activity Index (BASDAI), numerical pain rating scale (NRS), Hospital Anxiety and Depression Scale (HADS), Short Form 36 (SF-36), Evaluation of AS Quality of Life questionnaire (EASi-QoL) and ASES-AS. Respondents received repeat questionnaires at 2 weeks and 6 months including health transition questions assessing change in AS-specific and general health. The ASES-AS was assessed for data quality, reliability, validity, and responsiveness. RESULTS Response rate was 64% (n=612), 72% (n=438) were male, mean age 50.8yrs (SD 12.2 yrs), mean disease duration 17.3 yrs (SD 11.7 yrs) and mean symptom duration 22.4 yrs (SD 12.4 yrs). Missing data for each item/total score range was 0.7%-3.1%. Item-total correlations range was 0.66 to 0.83. Cronbach's alpha was 0.93 and test-retest reliability (intraclass correlation coefficient) 0.77. A priori hypothesised associations between ASAS-AS and disease status measures were supported. Social variables potentially related to self-efficacy demonstrated evidence of convergent validity (employment p<0.001, educational level p<0.005). A Modified Standard Response Mean (MSRM) of 0.44 and 0.26 in AS-specific and general health respectively at 6 months indicates moderate responsiveness. CONCLUSIONS ASES-AS has good evidence supporting its application as an AS-specific self-efficacy measure in research including clinical trials at a group level.