Comparative responsiveness of 3 functional indices in ankylosing spondylitis.
OBJECTIVE
To compare the responsiveness of the Bath Ankylosing Spondylitis Functional Index (BASFI), the Dougados Functional Index (DFI), and the ankylosing spondylitis-specific version of the Health Assessment Questionnaire (HAQ-S).


METHODS
Using data from a placebo controlled, randomized clinical trial we designed a responsiveness model including both hypothesized improvement (n = 39; continuous diclofenac treatment) and hypothesized deterioration (n = 40; patients who withdrew from the clinical trial because of a flare) of functional performance. Instrument responsiveness was examined using 4 statistics including standardized response mean (SRM), effect size (ES), the Guyatt method, and the variance method. Ceiling and floor effects were visualized using histograms for cross sectional and time-path diagrams for longitudinal analysis.


RESULTS
The BASFI ranked superior compared to the DFI and HAQ-S in detecting both improvement and deterioration of functional performance. All 4 responsiveness statistics consistently confirmed this superiority of the BASFI. However, the median baseline scores of all 3 questionnaires were close to the lower end of the instrument and the score distribution showed skewed patterns.


CONCLUSIONS
The BASFI appears to be more responsive than the DFI and the HAQ-S in situations of both improvement and deterioration of functional performance. However, addition of particular difficult items may improve the performance of the BASFI as well as of the other 2 instruments.
Ruof
J
J
Rheumaklinik und Institut für Physikalische Medizin, Zürich, Switzerland.
Sangha
O
O
Stucki
G
G
D000328:Adult; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage*; D004008:Diclofenac / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D017060:Patient Satisfaction; D011379:Prognosis; D016059:Range of Motion, Articular; D012008:Recurrence; D012016:Reference Values; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000175:diagnosis / Q000188:drug therapy* / Q000503:physiopathology; D016896:Treatment Outcome; D014801:Vitamin A / Q000008:administration & dosage*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D014801:Vitamin A; D004008:Diclofenac