This variable was considered as primary in all countries except for Canada (and any other country where applicable or where requested by Regulatory Authorities) where it was considered as secondary variable.

ASDAS-MI was achieved when there was a reduction (improvement) >= 2.0 in the ASDAS relative to Baseline, or when the lowest possible ASDAS score (0.6) was reached.

The ASDAS was calculated as the sum of the following components:

0.121 × Back pain (BASDAI Q2 result) 0.058 × Duration of morning stiffness (BASDAI Q6 result) 0.110 × Patient's Global Assessment of Disease Activity (PGADA) 0.073 × Peripheral pain/swelling (BASDAI Q3 result) 0.579 × (natural logarithm [ln] of the (CRP [mg/L] + 1)) Back pain, PGADA, duration of morning stiffness, peripheral pain/swelling and fatigue were all assessed on a numerical scale (0 to 10 units, where 0 is "not active" and 10 is "very active").

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

This variable was considered as primary for Canada (and any other country where applicable or where requested by Regulatory Authorities) and as secondary variable in all other countries.

The ASAS40 response was defined as relative improvements of at least 40 % and absolute improvement of at least 2 units on a 0 to 10 Numeric Rating Scale (NRS), where 0 is "not active" and 10 is "very active" in at least 3 of the 4 domains: Patient's Global Assessment of Disease Activity (PGADA), Pain assessment (total spinal pain NRS scores), Function (Bath Ankylosing Spondylitis Functional Index (BASFI), Inflammation (mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)) questions 5 and 6 concerning morning stiffness intensity and duration) and no worsening at all in the remaining domain.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

Certolizumab pegol plasma concentration was measured at Baseline in micrograms per millilitre (µg/mL).

The Safety Set (SS) consisted of all subjects who have received at least 1 dose of study medication. Note: None of the Safety Set subjects had Pharmacokinetic (PK) concentrations above the lower limit of quantification.

Certolizumab pegol plasma concentration was measured at Week 1, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment. Note: No samples taken at Week 1 for the Placebo->OL CZP.

Certolizumab pegol plasma concentration was measured at Week 2, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment. Note: No samples taken at Week 2 for the Placebo->OL CZP.

Certolizumab pegol plasma concentration was measured at Week 4, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment.

Certolizumab pegol plasma concentration was measured at Week 12, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment.

Certolizumab pegol plasma concentration was measured at Week 24, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment.

Certolizumab pegol plasma concentration was measured at Week 36, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment.

Certolizumab pegol plasma concentration was measured at Week 52, in µg/mL.

The SS consisted of all subjects who received at least 1 dose of study treatment. Note: No samples taken at OL Week 52 for the Placebo->OL CZP.

Certolizumab pegol plasma concentration was measured at the Follow-Up Visit, in µg/mL.

Follow-Up Visit was defined as 8 weeks after Week 52 or Withdrawal (WD) visit for subjects not participating in the Safety Follow-Up Extension (SFE) Period.

The SS consisted of all subjects who received at least 1 dose of study treatment. Only participants included, who had a SFU Visit at 8 weeks after Week 52/WD visit for those not participating in the SFE period.

The ASAS40 response was defined as relative improvements of at least 40% and absolute improvement of at least 2 units on a 0 to 10 Numeric Rating Scale (NRS), where 0 is "not active" and 10 is "very active" in at least 3 of the 4 domains: Patient's Global Assessment of Disease Activity (PGADA), Pain assessment (total spinal pain NRS scores), Function (Bath Ankylosing Spondylitis Functional Index (BASFI)), Inflammation (mean of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)) questions 5 and 6 concerning morning stiffness intensity and duration) and no worsening at all in the remaining domain.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The BASFI is a validated disease-specific instrument for assessing physical function. The BASFI comprises 10 items relating to the past week. The BASFI is the mean of the 10 scores such that the total score ranges from 0 (Easy) to 10 (Impossible), with lower scores indicating better physical function. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The BASFI is a validated disease-specific instrument for assessing physical function. The BASFI comprises 10 items relating to the past week. The BASFI is the mean of the 10 scores such that the total score ranges from 0 (Easy) to 10 (Impossible), with lower scores indicating better physical function. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The BASDAI is a validated self-reported instrument, which consists of six 10 unit horizontal Numeric Rating Scales to measure the disease activity of ankylosing spondylitis (AS) from the subject's perspective. It measures the severity of fatigue, spinal and peripheral joint pain and swelling, enthesitis, and morning stiffness (both severity and duration) over the last week. The final BASDAI scores ranges from 0 (not active) to 10 (very active), with lower scores indicating lower disease activity. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The BASDAI is a validated self-reported instrument, which consists of six 10 unit horizontal Numeric Rating Scales to measure the disease activity of ankylosing spondylitis (AS) from the subject's perspective. It measures the severity of fatigue, spinal and peripheral joint pain and swelling, enthesitis, and morning stiffness (both severity and duration) over the last week. The final BASDAI scores ranges from 0 (not active) to 10 (very active), with lower scores indicating lower disease activity. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The Spondyloarthritis Research Consortium of Canada (SPARCC) scoring method for lesions found on the Magnetic Resonance Imaging (MRI) is based on an abnormal increased signal on the Short-Tau-Inversion Recovery (STIR) sequence, representing bone marrow edema. Total Sacroiliac (SI) joint SPARCC score can range from 0 to 72 with higher scores indicating higher joint inflammation. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The number of subjects who did not have relevant changes to background medications during the study treatment period.

A subject is without relevant changes to background medication if they do not have: the addition of a new disease-modifying antirheumatic drug (DMARD) or the change from one DMAR to another; the addition of an nonsteroidal anti-inflammatory drug (NSAID) or the change from one NSAID to another; an increased dose of chronic corticosteroids; the addition of a new chronic analgesic medication or increased dose in chronic analgesic medication; and they complete double-blind study treatment to Week 52.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The ASQoL score ranged from 0 to 18 with higher score indicating worse Health-Related Quality of Life (HRQoL) and 0 indicating good HRQoL. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The nocturnal spinal pain experienced by subjects due to AS was measured by following question 'How much pain of your spine due to spondylitis do you have at night?'. The NRS ranged from 0 to 10, where 0 represented 'no pain' and 10 represented 'most severe pain'. The change from Baseline is calculated, a negative value indicating improvement and a positive value worsening.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

The number of subjects with AU or new AU flares during the study treatment period.

The FAS consisted of all subjects in the RS who have received at least 1 dose of study medication.

An Adverse Event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with this treatment. An AE could therefore be any unfavorable and unintended sign, symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product.

The SS consisted of all subjects who received at least 1 dose of study treatment.

A serious adverse event (SAE) is any untoward medical occurrence that at any dose:

• Results in death
• Is life-threatening
• Requires in patient hospitalization or prolongation of existing hospitalization
• Is a congenital anomaly or birth defect
• Is an infection that requires treatment parenteral antibiotics
• Other important medical events which based on medical or scientific judgement may jeopardize the patients, or may require medical or surgical intervention to prevent any of the above.

The SS consisted of all subjects who received at least 1 dose of study treatment.

An Adverse Event (AE) is any untoward medical occurrence in a patient or clinical investigation subject administered a pharmaceutical product, which does not necessarily have a causal relationship with this treatment. An AE could therefore be any unfavorable and unintended sign, symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product.

The SS consisted of all subjects who received at least 1 dose of study treatment.