title: Moving instead of asking? Performance-based tests and BASFI-questionnaire measure different aspects of physical function in ankylosing spondylitis.
abstract: BACKGROUND
  Ankylosing Spondylitis (AS) is characterised by limitations in physical function. The Bath Ankylosing Spondylitis Functional Index (BASFI) is considered to be the gold-standard to assess physical function in AS patients. However, the BASFI questionnaire is a self-reported outcome measure and susceptible to subjective interpretation (under- or over-estimation). More objective outcome measures, like performance-based tests, could provide an objective outcome measurement for the evaluation of limitations in physical function. Therefore, the primary aim of this study was to determine the association between performance-based measures and the BASFI questionnaire.
  
  
  METHODS
  In this cross-sectional study 126 AS patients completed the BASFI questionnaire and eight performance-based tests based on BASFI-items. Each test received three scores: one for performance (time or points) and a score for exertion and pain experienced during performance (using modified Borg-scale and VAS 0-100 mm, respectively). Linear regression analyses were used to assess the associations between the BASFI questionnaire and performance-based tests.
  
  
  RESULTS
  The univariable association between performance and BASFI-score was moderate with a R-square of 0.31 and Beta of 0.56 (p's < 0.05). In a multivariable analysis, the association between performance, exertion and pain on the one hand and BASFI-score on the other was assessed; R-square increased to 0.54: the Beta's for exertion and pain during performance were 0.38 and 0.26, respectively; the Beta for performance decreased to 0.19 (p's < 0.05).
  
  
  CONCLUSIONS
  This study demonstrates that alongside actual performance, patients seem to incorporate exertion and pain in their assessment of perceived physical function on the BASFI questionnaire. Performance-based tests could provide an objective outcome measurement for the evaluation of physical function and give relevant new information in addition to the BASFI questionnaire.
authors.affiliation: Reade, Centre for Rehabilitation and Rheumatology, Dr, Jan van Breemenstraat 2, PO Box 58271, 1040 HG Amsterdam, the Netherlands. s.v.weely@reade.nl
authors.forename: Salima F E
authors.initials: SF
authors.lastname: van Weely
authors.forename: J Christiaan
authors.initials: JC
authors.lastname: van Denderen
authors.forename: Martijn P M
authors.initials: MP
authors.lastname: Steultjens
authors.forename: Marike
authors.initials: M
authors.lastname: van der Leeden
authors.forename: Michael T
authors.initials: MT
authors.lastname: Nurmohamed
authors.forename: Joost
authors.initials: J
authors.lastname: Dekker
authors.forename: Ben A C
authors.initials: BA
authors.lastname: Dijkmans
authors.forename: Irene E
authors.initials: IE
authors.lastname: van der Horst-Bruinsma
mesh_terms: D000203:Activities of Daily Living / Q000523:psychology*; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods / Q000592:standards; D011597:Psychomotor Performance; D057566:Self Report / Q000592:standards*; D013167:Spondylitis, Ankylosing / Q000175:diagnosis* / Q000503:physiopathology* / Q000523:psychology*; D011795:Surveys and Questionnaires / Q000592:standards*