PASI-75 response is the percentage of participants who achieved at least a 75% reduction (improvement) from baseline in PASI score at week 16. The improvement in PASI score was used as a measure of efficacy. The PASI is a measure of psoriatic disease severity taking into account qualitative lesion characteristics (erythema, thickness, and scaling) and degree of skin surface area involvement on defined anatomical regions. PASI scores range from 0 to 72, with higher scores reflecting greater disease severity. Erythema, thickness, and scaling are scored on a scale of 0 (none) to 4 (very severe) on 4 anatomic regions of the body: head, trunk, upper limbs, and lower limbs. Degree of involvement on each of the 4 anatomic regions is scored on a scale of 0 (no involvement) to 6 (90% to 100% involvement). The PASI score was set to missing if any severity score or degree of involvement is missing.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward (LOCF) imputation was used. .

The sPGA was a 5-point scale ranging from 0 (clear), 1 (almost clear), 2 (mild), 3 (moderate), to 4 (severe), incorporating an assessment of the severity of the three primary signs of the disease: erythema, scaling and plaque elevation. When making the assessment of overall severity, the Investigator must have factored in areas that have already been cleared (ie, have scores of 0) and not just evaluate remaining lesions for severity, ie, the severity of each sign was averaged across all areas of involvement, including cleared lesions. In the event of different severities across disease signs, the sign that is the predominant feature of the disease should be used to help determine the sPGA score.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used.

BSA was a measurement of involved skin. The overall BSA affected by psoriasis was estimated based on the palm area of the participant's hand (entire palmar surface or "handprint" including the fingers), which equates to approximately 1% of total body surface area.

BSA percent change from baseline (Visit 2 Week 0) was determined at each visit of the study, which is calculated as 100*(visit BSA - baseline BSA) / baseline BSA (%).

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Participants with a baseline value and at least 1 postbaseline value were included. Last observation carried forward imputation was used.

Psoriasis Area Severity Index (PASI) scores range from 0 to 72, with higher scores reflecting greater disease severity. Erythema, thickness, and scaling are scored on a scale of 0 (none) to 4 (very severe) on 4 anatomic regions of the body: head, trunk, upper limbs, and lower limbs. Degree of involvement on each of the 4 anatomic regions is scored on a scale of 0 (no involvement) to 6 (90% to 100% involvement). The total qualitative score (sum of erythema, thickness, and scaling scores) is multiplied by the degree of involvement for each anatomic region and then multiplied by a constant. These values for each anatomic region are summed to yield the PASI score. The PASI score was set to missing if any severity score or degree of involvement is missing.

FAS consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward (LOCF) imputation was used. Participants with a baseline value and at least 1 postbaseline value are included.

PASI-50 response is the percentage of participants who achieved at least a 50% reduction (improvement) from baseline in PASI score at Week 16. The improvement in PASI score was used as a measure of efficacy. The PASI is a measure of psoriatic disease severity taking into account qualitative lesion characteristics (erythema, thickness, and scaling) and degree of skin surface area involvement on defined anatomical regions. PASI scores range from 0 to 72, with higher scores reflecting greater disease severity. Erythema, thickness, and scaling are scored on a scale of 0 (none) to 4 (very severe) on 4 anatomic regions of the body: head, trunk, upper limbs, and lower limbs. Degree of involvement on each of the 4 anatomic regions is scored on a scale of 0 (no involvement) to 6 (90% to 100% involvement). The PASI score was set to missing if any severity score or degree of involvement is missing.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used.

The Pruritus Visual Analog Scores (VAS) were used to measure the amount of itching and discomfort a participant experiences. Participant's Assessment of Pruritus (Itch) asked: On average, how much itch have you had because of your condition in the past week? All VAS values range from 0 to 100. Higher scores correspond to more severe symptom or disease. Change from baseline was calculated for the VAS scale, where change = visit value - baseline value.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used. Participants with a baseline value and at least 1 postbaseline value are included.

DLQI is a simple, compact, and practical questionnaire for use in a dermatology clinical setting to assess limitations related to the impact of skin disease. The instrument contains ten items dealing with the participant's skin. With the exception of Item Number 7, the participant responds on a four-point scale, ranging from "Very Much" (score 3) to "Not at All" or "Not relevant" (score 0). Item Number 7 is a multi-part item, the first part of which ascertains whether the participant's skin prevented them from working or studying (Yes or No, scores 3 or 0 respectively), and if "No," then the subject is asked how much of a problem the skin has been at work or study over the past week, with response alternatives being "A lot," "A little," or "Not at all" (scores 2, 1, or 0 respectively). The DLQI total score was derived by summing all item scores, which has a possible range of 0 to 30, with 30 corresponding to the worst quality of life, and 0 corresponding to the best.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used. Participants with a baseline value and at least 1 postbaseline value are included

The SF-36 was a 36-item general health instrument and consists of 8 scales: physical function (PF), role limitations-physical (RP), vitality (VT), general health perceptions (GH), bodily pain (BP), social function (SF), role limitations-emotional (RE), and mental health (MH). Scale scores range from 0 to 100, with higher scores indicating better health. Two overall summary scores were obtained - a Physical Component Summary score (PCS) and a Mental Component Summary score (MCS).

Scores from the 8 scales, PCS and MCS were transformed to the norm-based scores using weights from U.S. general population, with 50 as the average and 10 as the standard deviation, higher scores indicating better health. For norm based scores, change from baseline were calculated for the 8 scales and the two summary scales, where change = visit value - baseline value.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used. Participants with a baseline value and at least 1 postbaseline value are included.

PASI-75 response is the percentage of participants who achieved at least a 75% reduction (improvement) from baseline in PASI score at Week 16. The improvement in PASI score was used as a measure of efficacy. See Outcome measure #1 for further description.

sPGA is a 5-point scale ranging from 0 (clear), 1 (almost clear), 2 (mild), 3 (moderate), to 4 (severe), incorporating an assessment of the severity of the three primary signs of the disease: erythema, scaling and plaque elevation. See Outcome Measure #2 for further description.

The Full Analysis Set (FAS) consisted of all participants who were randomized per protocol. Participants were included in the treatment group to which they were randomized APR 30 BID or placebo for the FAS. Last observation carried forward imputation was used.

Time to loss was the time between the re-randomization date and the date of the first assessment with loss of 50% PASI improvement (event), or the time between the re-randomization date and the date of the last PASI assessment in the randomized withdrawal phase prior to addition of topical/phototherapy or other effective psoriasis therapies, or resumption of apremilast 30 mg BID, or discontinuation, or Week 52 if no loss (censored), whichever was earlier

Analysis population consisted of participants who were re-randomized to placebo or Apremilast 30mg BID at Week 32.

An AE was any noxious, unintended, or untoward medical occurrence, that may appear or worsen in a participant during the course of study. It may be a new intercurrent illness, a worsening concomitant illness, an injury, or any concomitant impairment of the participant's health, including laboratory test values regardless of etiology. Any worsening (ie, any clinically significant adverse change in the frequency or intensity of a preexisting condition) was considered an AE. A serious AE (SAE) is any untoward adverse event that is fatal, life-threatening, results in persistent or significant disability or incapacity, requires or prolongs existing in-patient hospitalization, is a congenital anomaly/birth defect, or is a condition that may jeopardize the patient or may require intervention to prevent one of the outcomes listed above. An AE is a treatment emergent AE if the AE start date is on or after the date of the first dose of study drug and no later than 28 days after the last dose.

Safety population consisted of all participants who were randomized and received at least one dose of Investigational Product (IP)

Psoriasis flare was defined as a sudden intensification of psoriasis requiring medical intervention, or a diagnosis of new generalized erythrodermic, inflammatory, or pustular psoriasis. Rebound is defined as a severe and sudden worsening of disease that occurs after treatment has been discontinued. Note categories below. [1] Psoriasis adverse events (ie, preferred term as Guttate psoriasis, Psoriasis, Pustular psoriasis) started on or after the first dose date and on or before the last dose date within the phase. [2] Psoriasis adverse events (ie, preferred term as Guttate psoriasis, Psoriasis, Pustular psoriasis, Rebound psoriasis) started after the last dose date for participants who discontinued within the phase. [3] PASI >= 125% of baseline score at any visit after the last dose date for participants who discontinued within the phase and were not included in [1] and/or [2].

Safety population, included all participants who were randomized and received at least one dose of IP. Participants with a PASI ≥ 125% of Baseline score after last dose who did not have psoriasis rebound captured as a Treatment Emergent Adverse Event.

The Apremilast-exposure Period started on the date of the first dose of apremilast (Week 0 for participants originally randomized to apremilast or Week 16 for participants originally randomized to placebo) to the last dose of apremilast. Adverse events that started after 28 days of initiating placebo and before resuming apremilast treatment in the Randomized Treatment Withdrawal Phase (Weeks 32 to 52) were excluded in the Apremilast-exposure phase. A serious AE (SAE) is any untoward adverse event that is fatal, life-threatening, results in persistent or significant disability or incapacity, requires or prolongs existing in-patient hospitalization, is a congenital anomaly or birth defect, or a condition that may jeopardize the patient or may require intervention to prevent one of the outcomes listed above. An AE is a treatment emergent AE if the AE start date is on or after the date of the first dose of study drug and no later than 28 days after the last dose.

Apremilast participants as treated, which includes all participants who were randomized to (at Week 0) or treated with (at Week 16) apremilast 30 mg BID, and received at least one dose of apremilast after randomization or Week 16.

Psoriasis flare was defined as a sudden intensification of psoriasis requiring medical intervention, or a diagnosis of new generalized erythrodermic, inflammatory, or pustular psoriasis. Rebound is defined as a severe and sudden worsening of disease that occurs after treatment has been discontinued. Note categories below. [1] Psoriasis adverse events (ie, preferred term as Guttate psoriasis, Psoriasis, Pustular psoriasis) started on or after the first dose date and on or before the last dose date within the phase. [2] Psoriasis adverse events (ie, preferred term as Guttate psoriasis, Psoriasis, Pustular psoriasis, Rebound psoriasis) started after the last dose date for participants who discontinued within the phase. [3] PASI >= 125% of baseline score at any visit after the last dose date for participants who discontinued within the phase and were not included in [1] and/or [2].

The apremilast subjects as treated population, which includes all participants who were randomized to (at Week 0) or treated with (at Week 16) apremilast 30 mg BID, and received at least one dose of apremilast after randomization or Week 16.