The sPGA is the physician's determination of the participant's psoriasis (PsO) lesions overall at a given time point. Lesions were categorized by descriptions for induration, erythema, and scaling. Participant's PsO was assessed as 0 (clear), 1 (minimal), 2 (mild), 3 (moderate), 4 (severe), or 5 (very severe). An sPGA responder was defined as having a post-baseline sPGA score of "0" or "1" with at least a 2-point improvement from baseline.

Induction Period: All randomized participants.

PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs) and the severity of scaling, redness, and plaque induration/infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis (PsO) to 72 for the most severe disease. For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored separately and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs (0.4)]. Overall scores range from 0 (no PsO) to 72 (the most severe disease).

Induction Period: All randomized participants.

PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs) and the severity of scaling, redness, and plaque induration/infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis (PsO) to 72 for the most severe disease. For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored separately and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs (0.4)]. Overall scores range from 0 (no PsO) to 72 (the most severe disease).

Induction Period: All randomized participants.

PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs) and the severity of scaling, redness, and plaque induration/infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis (PsO) to 72 for the most severe disease. For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored separately and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs (0.4)]. Overall scores range from 0 (no PsO) to 72 (the most severe disease).

Induction Period: All randomized participants.

PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs) and the severity of scaling, redness, and plaque induration/infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis (PsO) to 72 for the most severe disease. For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored separately and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs (0.4)]. Overall scores range from 0 (no PsO) to 72 (the most severe disease).

Induction Period: All randomized participants.

The BSA is the percentage involvement of psoriasis on each participant's body surface on a continuous scale from 0% (no involvement) to 100% (full involvement), in which 1% corresponds to the size of the participant's hand (including the palm, fingers, and thumb). The total BSA affected was the summation of individual regions affected. Percentage response is calculated by number of participants with a response divided by number of participants with non-missing values multiplied by 100.

Induction Period:All randomized participants.

PSS is a patient-administered assessment of 4 symptoms (itch, pain, stinging, and burning); 3 signs (redness, scaling, and cracking); and 1 item on the discomfort related to symptoms/signs. The overall severity for each individual symptom/sign from the patient's psoriasis is indicated by selecting the number from a numeric rating scale (NRS) of 0 to 10 that best describes the worst level of each symptom/sign in the past 24 hours, where 0=no symptom/sign and 10=worst imaginable symptom/sign. In addition, a symptoms score ranging from 0 (no symptoms) to 40 (worst imaginable symptoms), and a signs score of 0 (no signs) to 30 (worst imaginable signs) will be reported. Percentage response is calculated by number of participants with a response divided by number of participants with non-missing values multiplied by 100.

Induction Period: All randomized participants who had PSS symptoms score ≥1 at baseline.

The DLQI is a patient-reported, 10-question, quality-of-life questionnaire that covers 6 domains including symptoms and feelings, daily activities, leisure, work and school, personal relationships, and treatment. Response categories include "Not at all," "A little," "A lot," and "Very much," with corresponding scores of 0, 1, 2, and 3 respectively. Questions 3-10 also have an additional response category of "Not relevant" which is scored as "0". For all questions, if unanswered the question is scored as "0". Totals range from 0 to 30 (less to more impairment). A DLQI total score of 0 to 1 is considered as having no effect on a patient's health-related quality of life (HRQoL), and a 5-point change from baseline is considered as the minimal clinically important difference (MCID) threshold. Percentage response is calculated by number of participants with a response divided by number of participants with non-missing values multiplied by 100.

Induction Period: All randomized participants who had a baseline DLQI Total Score ≥5

PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs) and the severity of scaling, redness, and plaque induration/infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis (PsO) to 72 for the most severe disease. For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored separately and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs (0.4)]. Overall scores range from 0 (no PsO) to 72 (the most severe disease).

Maintenance Period: All re-randomized participants who were responders (≥PASI 90).

The Palmoplantar PASI is a composite score derived from the sum scores for erythema, induration, and desquamation multiplied by a score for the extent of palm and sole area involvement, ranging from 0 (no PPASI) to 72 (most severe PPASI). The PPASI was only assessed if participants have palmoplantar psoriasis at baseline. Least Squares Mean (LS Mean) was calculated using mixed model repeated measures (MMRM) model with treatment, baseline value, visit, the interaction of the baseline value-by-visit, the interaction of treatment by-visit, and previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as covariates.

Induction Period: All randomized participants who had palmoplantar involvement at baseline.

The PSSI is a physician assessment of erythema, induration and desquamation and percent of scalp that is covered with a scores range from 0 (none) to 4 (very severe). The composite score is derived from the sum of scores for erythema, induration, and desquamation multiplied by the score recorded for the extent of the scalp area involved, 1 (<10%) to 6 (90%-100%) with a total score ranging from 0 (less severity) to 72 (more severity). LS Mean was calculated using MMRM model with treatment, baseline value, visit, the interaction of the baseline value-by-visit, the interaction of treatment by-visit, and previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as covariates.

Induction Period: All randomized participants who had scalp Involvement at baseline.

The NAPSI scale is used to evaluate the severity of fingernail bed Ps and fingernail matrix PsO by area of involvement. The fingernail is divided into quadrants. Each fingernail is given a score for fingernail bed PsO 0 (none) to 4 (PsO in 4 quadrants of the fingernail) and fingernail matrix PsO 0 (none) to 4 (Ps in 4 quadrants of the matrix), depending on the presence (score of 1) or absence (score of 0) of any of the features of fingernail bed or matrix PsO in each quadrant. The sum of all fingernails equals the total NAPSI score range is from 0 (no effect) to 80 (more severe psoriasis). LS Mean was calculated using MMRM model with treatment, baseline value, visit, the interaction of the baseline value-by-visit, the interaction of treatment by-visit, and previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as covariates.

Induction Period: All randomized participants who had Nail Psoriasis involvement at baseline.

SF-36 consists of 36 questions measuring 8 health domains: physical functioning, bodily pain, role limitations due to physical problems, role limitations due to emotional problems, general health perceptions, mental health, social function, and vitality. The patient's responses are solicited using Likert scales that vary in length, with 3-6 response options per item. The SF-36 can be scored into the 8 health domains named above and two overall summary scores: physical component summary (PCS) and mental component summary (MCS) scores. The domain and summary scores range from 0 to 100; higher scores indicate better levels of function and/or better health. LS Mean was calculated using Analysis of covariance (ANCOVA) model with treatment and baseline value, previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as fixed factors.

Induction Period: All randomized participants who had a baseline and at least one post-baseline PCS value.

SF-36 consists of 36 questions measuring 8 health domains: physical functioning, bodily pain, role limitations due to physical problems, role limitations due to emotional problems, general health perceptions, mental health, social function, and vitality. The patient's responses are solicited using Likert scales that vary in length, with 3-6 response options per item. The SF-36 can be scored into the 8 health domains named above and two overall summary scores: physical component summary (PCS) and mental component summary (MCS) scores. The domain and summary scores range from 0 to 100; higher scores indicate better levels of function and/or better health. LS Mean was calculated using Analysis of covariance (ANCOVA) model with treatment and baseline value, previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as fixed factors.

Induction Period: All randomized participants who had a baseline and at least one post-baseline MCS value.

The PatGA is a single-item self-reported instrument asking the participant to rate the severity of their psoriasis "today" by circling a number on the numeric rating scale from 0 (Clear = no psoriasis) to 5 (Severe = the worst their psoriasis has ever been). Percentage response is calculated by number of participants with a response divided by number of participants with non-missing values multiplied by 100.

Induction Period: All randomized participants who had a baseline >= 2.

The WPAI-PSO consists of 6 questions to determine employment status, hours missed from work because of psoriasis, hours missed from work for other reasons, hours actually worked, the degree to which psoriasis affected work productivity while at work, and the degree to which psoriasis affected activities outside of work. Four scores are derived: absenteeism, presenteeism (reduced productivity while at work), an overall work impairment score that combines absenteeism and presenteeism and impairment in activities performed outside of work. Each WPAI score is expressed as impairment percentages (0-100) with higher numbers indicating greater impairment and less productivity, that is, worse outcomes. LS Mean was calculated using Analysis of covariance (ANCOVA) model with treatment and baseline value, previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as fixed factors.

Induction Period:All randomized participants who had a baseline and at least one post-baseline WPAI-PSO value.

QIDS-SR16 is a participant-administered, 16-item instrument intended to assess the existence and severity of symptoms of depression. A participant is asked to consider each statement as it relates to the way they have felt for the past 7 days and rate each on a 4-point scale: 0 (best) to 3 (worst). The sum of the 16 items corresponding to 9 depression domains [sad mood, concentration, self-criticism, suicidal ideation, interest, energy/fatigue, sleep disturbance (initial, middle and late insomnia or hypersomnia), decrease/increase in appetite/weight, and psychomotor agitation/retardation] to give a single total scores range from 0 to 27, with higher scores indicating greater symptom severity. Whereas 0-5 indicates no symptoms. LS Mean was calculated using ANCOVA model with treatment and baseline value, previous exposure to biologic therapy (yes/no), body weight (<100 kg or >=100 kg), and geographic region (North America or Other) as fixed factors.

Induction Period: All participants who received at least one dose of study drug who had a baseline QIDS-SR16 total score >=11.

The DLQI is a patient-reported, 10-question, quality-of-life questionnaire that covers 6 domains including symptoms and feelings, daily activities, leisure, work and school, personal relationships, and treatment. Response categories include "Not at all," "A little," "A lot," and "Very much," with corresponding scores of 0, 1, 2, and 3 respectively. Questions 3-10 also have an additional response category of "Not relevant" which is scored as "0". For all questions, if unanswered the question is scored as "0". Totals range from 0 to 30 (less to more impairment). A DLQI total score of 0 to 1 is considered as having no effect on a patient's health-related quality of life (HRQoL), and a 5-point change from baseline is considered as the minimal clinically important difference (MCID) threshold. Percentage response is calculated by number of participants with a response divided by number of participants with non-missing values multiplied by 100.

Induction Period: All randomized participants who had a baseline and at least one post-baseline DLQI value.

Minimum observed serum concentration at steady state (Ctrough,ss) of mirikizumab at Week 16.

Induction Period: All participants who received at least one dose of study drug who had evaluable PK data.