Table 4.

Interactions with baseline characteristics and spinal radiographic progression with generalized estimating equations model (n=101)

Variable	Univariate analysis			Multivariable analysis
	β (95% CI)	p-value		β (95% CI)	p-value
Time	1.68 (1.04∼2.32)	<0.001		−1.22 (−4.71∼2.28)	0.494
Time*female	−1.44 (−2.18∼−0.70)	<0.001		−1.40 (−2.27∼−0.54)	0.001
Time*current smoker	−0.19 (−0.18∼1.10)	0.772
Time*uveitis	−0.22 (−1.52∼1.08)	0.738
Time*enthesitis	−1.04 (−1.87∼−0.22)	0.013		0.29 (−0.43∼1.01)	0.430
Time*peripheral arthritis	−1.24 (−2.33∼−0.16)	0.025		−0.37 (−1.29∼0.56)	0.438
Time*hip arthritis	−0.23 (−1.65∼1.19)	0.749
Time*anti TNF use	−0.26 (−2.42∼1.90)	0.811
Time*leptin/100	−0.01 (−0.02∼0.01)	0.472
Time*Dkk1/100	−0.11 (−0.03∼−2.69)	0.007		−0.11 (−0.13∼−0.06)	<0.001
Time*estrogen	−0.01 (−0.03∼0.01)	0.313
Time*age at symptom onset	0.07 (0.03∼0.12)	0.002		0.03 (−0.01∼0.07)	0.098
Time*initial ESR	0.01 (−0.01∼0.02)	0.421
Time*initial CRP	0.23 (0.08∼0.39)	0.003		0.11 (−0.01∼0.22)	0.059
Time*BMI	0.20 (0.05∼0.36)	0.011		0.12 (0.01∼0.25)	0.047
Time*initial mSASSS	0.04 (−0.02∼0.09)	0.186		0.00 (−0.01∼0.02)	0.798

TNF: tumor necrosis factor, Dkk1: dickkopf-1, ESR: erythrocyte sedimentation rate, CRP: C-reactive protein, BMI: body mass index, mSASSS: modified Stoke Ankylosing Spondylitis Spine Score, CI: confidence interval.