Variable* | High educational attainment, male patients only | Low educational attainment, male patients only | ||||||||||
Model ASDAS (n=34) | Model BASDAI (n=35) | Model BASFI (n=33) | Model ASDAS (n=62) | Model BASDAI (n=65) | Model BASFI (n=64) | |||||||
HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | HR | 95% CI | |
Age, years | 0.98 | 0.92 to 1.04 | 0.98 | 0.93 to 1.03 | 1.00 | 0.95 to 1.05 | 1.04 | 1.00 to 1.08 | 1.04 | 1.00 to 1.07 | 1.01 | 0.97 to 1.05 |
ASDAS-CRP | 0.92 | 0.59 to 1.45 | 1.67 | 1.23 to 2.28 | ||||||||
BASDAI | 0.81 | 0.60 to 1.10 | 1.33 | 1.18 to 1.51 | ||||||||
BASFI | 0.59 | 0.32 to 1.07 | 1.17 | 1.02 to 1.34 |
Due to correlation/collinearity between ASDAS, BASDAI and BASFI, it was decided to perform three separate analyses for these variables.
Procedure of variable selection: (1) P≥0.20 in univariable analysis and no confounder: country of origin, part-time worker, symptom duration, hip involvement, IBD, uveitis, NSAID index, csDMARD use, CRP, ESR, BAS-G, peripheral pain, swollen joint count. (2) P<0.20 in univariable analysis and/or a confounder for sex or age, but not significant within variable group: (group 1) job type; (group 2) comorbidity index, HLA-B27, psoriasis, smoking; (group 3) axial pain (ASDAS and BASDAI model), physician global, tender joint count; (group 4) BASMI, mSASSS. (3) Statistically significant within variable group, but not when included in final model: axial pain (BASFI model). (4) Excluded from analysis: CRP/ESR (excluded from ASDAS model due to overlap with ASDAS).
*Baseline values were used for all variables in this analysis.
AS, ankylosing spondylitis; ASDAS, AS Disease Activity Score; BASDAI, Bath AS Disease Activity Index; BASFI, Bath AS Functional Index; BAS-G, Bath AS Global Score; CRP, C reactive protein; ESR, erythrocyte sedimentation rate; HLA-B27, human leucocyte antigen B27; IBD, inflammatory bowel disease; NSAID, non-steroidal anti-inflammatory drug; csDMARD, conventional synthetic disease-modifying antirheumatic drug; mSASSS, modified Stoke Ankylosing Spondylitis Spine Score.