Evaluation of the Greek version of the Bath Ankylosing Spondylitis Functional Index: reliability, validity, and factor analysis.

OBJECTIVE To translate the Bath Ankylosing Spondylitis Functional Index (BASFI) into Greek, and validate its psychometric properties for the Greek patient population. Also, to assess the degree to which questions in the scale did address common themes, using confirmatory factor analysis. METHODS BASFI has been translated into Greek (BASFI-GrV), applied to 61 patients with ankylosing spondylitis, and validated as follows: a) Cronbach's alpha for the estimation of the internal consistency. b) Spearman's correlation coefficient for the assessment of test-retest reliability. c) Spearman's correlation coefficient for the assessment of concurent validity against the Hospital Anxiety and Depression Scale (HADS). d) Factor analysis. RESULTS The results showed the following: a) The BASFI-GrV demonstrated good internal consistency (alpha: 0.75). b) Test-retest scores produced no significant difference (p = 0.07). Spearman's rho correlation coefficient for test-retest was high on average (r = 0.91, p < 0.001), and ranged from 0.56 to 0.94 for each item. c) Spearman's rho between BASFI-GrV and HADS was 0.43 (p < 0.001). d) Factor analysis identified three factors with Eigen values ranging from 1.01 to 4.71, explaining totally 67.9 % of the variance. CONCLUSION Our findings indicate that BASFI-GrV is a valid and reliable questionnaire that can be used to evaluate the functional status of Greek patients with ankylosing spondylitis.