Table 2 Correlation of the three factors resulting from the principal components analysis with the variables in ISSAS database (results for candidate index A, including all items selected in the Delphi exercise excluding BASFI)
1 Patient-reported outcomes2 Peripheral activity3 Laboratory
Back pain at night0.840.100.05
Total spinal pain0.880.150.02
Patient global assessment0.820.210.15
BASDAI question 10.730.240.00
BASDAI question 20.860.110.05
BASDAI question 30.390.660.11
BASDAI question 60.660.110.09
Swollen joint count−0.050.860.17
Tender entheses count0.310.57−0.03
  • BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; ISSAS, International Study on Starting TNF blocking agents in Ankylosing Spondylitis; TNF, tumour necrosis factor.