ASAS, Assessment of Spondyloarthritis international Society Health Index scores range from 0 to 17, higher scores indicate worse health status; ASDAS, Ankylosing Spondylitis Disease Activity Score (scores range from 0.6 to 8, determined by the level of CRP or ESR (8 is the approximate maximum, given a CRP of 200), higher scores signify higher disease activity); axSpA, axial spondyloarthritis; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index (scores range from 0 to 10, higher scores signify higher disease activity); BASFI, Bath Ankylosing Spondylitis Functional Index (scores range from 0 to 10, higher scores signify greater impairment); COAST-V, a randomised placebo-controlled trial assessing efficacy and safety of ixekizumab for patients with radiographic axSpA; COAST-X, a randomised placebo-controlled trial assessing efficacy and safety of ixekizumab for patients with non-radiographic axSpA; CRP, C reactive protein (measured in mg/dL); ICC, intraclass correlation coefficient; MCID, minimal clinically important difference; MCII, minimal clinically important improvement; Night pain, Nocturnal back pain in the past week measured using an NRS scale (scores range from 0 to 10, higher scores indicating more pain); nr-axSpA, non-radiographic axSpA; Patient global, PtGA of disease activity measured using an NRS scale (scores range from 0 to 10, higher scores indicate worse health); RAPID-axSpA, a randomised placebo-controlled trial assessing efficacy and safety of certolizumab pegol for patients with radiographic and non-radiographic axSpA; r-axSpA, radiographic axSpA; SDC, smallest detectable change; SDD, SD of the mean difference of the two assessments; SF-36 PCS, Physical Component Summary of the Medical Outcomes Study 36-item Short-Form Health Survey (scores range from 0 to 100, higher scores indicate better health); SF-36 MCS, Mental Component Summary of the Medical Outcomes Study 36-item Short-Form Health Survey (scores range from 0 to 100, higher scores indicate better health); Total back pain, in the past week measured using an NRS scale (scores range from 0 to 10, higher scores indicating more pain).

*PtGA was only assessed at baseline, and baseline values were used to calculate ASDAS at both time points, meaning variability in PtGA was not considered and reliability of the ASDAS may be artificially improved.

†Calculated from the SDD using the formula SDC=1.96×SDD/(√2 x √2).

‡Score range 0–10, with three anchors: ‘0 hours’ (score 0), ‘1 hour’ (score 5) and ‘2 or more hours’ (score 10).

ASAS, Assessment of Spondyloarthritis international Society; ASDAS, Ankylosing Spondylitis Disease Activity Score; axSpA, axial spondyloarthritis; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; CRP, C reactive protein; ICC, intraclass correlation coefficient; MCID, minimal clinically important difference; MCII, minimal clinically important improvement; MCS, Mental Component Summary; nr-axSpA, non-radiographic axSpA; NRS, Numeric Rating Scale; PCS, Physical Component Summary; PtGA, patient global assessment; r-axSpA, radiographic axSpA; SDC, smallest detectable change; SDD, SD of the mean difference; SF-36, 36-item Short-Form Health Survey.