Statistical methods
sacroiliitis
SACROILIITIS
The change from baseline in the total sacroiliitis score and mSASSS score was calculated based on the average of scores assigned by 2 or 3 readers (if available) and presented as a cumulative probability of change from baseline. For binary variables (mNY criteria and syndesmophyte status), the analysis was carried out using a single-reader approach or 2-reader agreement approach. The single-reader approach considered a patient to be mNY criteria-positive when assessed mNY-positive by at least 1 reader. Correspondingly, if at least 1 reader assessed a vertebral unit as 2 or 3, the patient was considered to have a syndesmophyte. The 2-reader agreement approach considered a patient to be mNY criteria-positive or having a syndesmophyte when at least 2 readers assessed the patient as such.Inter-rater reliability was calculated by intraclass correlation coefficient (ICC), based on 2 reading scores made on the same subject by the primary readers. The smallest detectable change (SDC) was calculated using the Bland–Altman analysis at an 80% level of agreement (LoA) based on the data from the 2 primary readers [The full analysis set from week 104 database lock (final reading campaign) was used for the analysis. Data from the secukinumab loading and non-loading dose groups were pooled for this imaging post hoc analysis. Data are presented as observed.For radiographs, data are presented according to their original assignment at randomization with patients who switched to standard of care included as originally randomized and placebo patients who switched to secukinumab included in the placebo-secukinumab group. Patients who switched from blinded to open-label secukinumab 150 mg were included and presented as originally randomized (secukinumab group). For MRI, patients originally randomized to placebo who switched to active treatment were not included in the analysis. Patients randomized to secukinumab 150 mg blinded who switched to open-label secukinumab 150 mg were included and presented as originally randomized.