The sPGA is a 5-point scale where 0 = clear, 1 = almost clear, 2 = mild, 3 = moderate, and 4 =severe. Scores incorporate an assessment by the Investigator of the severity of the 3 primary signs of the disease: erythema, scaling and plaque elevation.

An sPGA response is defined as sPGA score of clear (0) or almost clear (1) and with at least a 2-point reduction from baseline at Week 16.

Intent-to-treat (ITT) analysis set: all participants who were randomized into the placebo controlled phase.

The BSA is a measurement of involved skin over the whole body. The overall BSA affected by psoriasis is estimated based on the palm area of the participant's hand. The surface area of the whole body is made up of approximately 100 palms or "handprints" (each entire palmar surface or "handprint" equates to approximately 1% of total body surface area).

ITT analysis set: all participants who were randomized in the placebo-controlled phase.

The BSA is a measurement of involved skin over the whole body. The overall BSA affected by psoriasis is estimated based on the palm area of the participant's hand. The surface area of the whole body is made up of approximately 100 palms or "handprints" (each entire palmar surface or "handprint" equates to approximately 1% of total body surface area).

A negative change from baseline indicates a reduction of affected BSA.

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with a baseline value and at least one post-baseline value at Week 16

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. 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.

PASI scores range from 0 to 72, with higher scores reflecting greater disease severity.

A negative change from baseline indicates an improvement of disease symptoms.

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with a baseline value and at least one post-baseline value at Week 16

The BSA is a measurement of involved skin over the whole body. The overall BSA affected by psoriasis is estimated based on the palm area of the participant's hand. The surface area of the whole body is made up of approximately 100 palms or "handprints" (each entire palmar surface or "handprint" equates to approximately 1% of total body surface area).

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with baseline BSA > 3%.

The whole body itch NRS is a self-reported measure where participants were asked to assess whole body itch and select a number on a scale of 0-10, where 0 represents no itch, and 10 represents the worst imaginable itch. A reduction in score from baseline represents an improvement in symptoms.

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with baseline whole body itch NRS score ≥ 4.

The ScPGA is a 5-point scale ranging from 0 (clear) to 4 (severe), incorporating an Investigator's assessment of the severity of the three primary signs of the disease: erythema, scaling and plaque elevation of the overall scalp.

An ScPGA response is defined as and ScPGA score clear (0) or almost clear (1) with at least a 2-point reduction from baseline among participants with a baseline ScPGA score ≥ 2.

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with baseline ScPGA Score ≥ 2).

The DLQI is a 10 item questionnaire dealing with the participant's skin. With the exception of Item Number 7, the participant responds on a four-point scale, ranging from 0 (not at all) to 3 (very much). 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), 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 0 (not at all), 1 (a little) and 2 (a lot).

Total scores have a possible range of 0 to 30, with 30 corresponding to the worst health-related quality of life, and 0 corresponding to the best score.

A negative change from baseline indicates an improvement in health-related quality of life scores.

ITT analysis set (all participants who were randomized) in the placebo-controlled phase with a baseline value and at least one post-baseline value at Week 16

An adverse event (AE) is An AE is any noxious, unintended, or untoward medical occurrence that may appear or worsen in a participant during the course of a study. A TEAE is any AE that occurs following administration of study treatment.

Frequency of TEAEs was assessed as well as severity and treatment relatedness.

A TEAE was considered severe based on the Investigator's assessment. A TEAE could be severe if it was serious or non-serious, had symptoms causing discomfort or pain, requiring medical or surgical attention or intervention, interfered with activities of daily life and if drug therapy was required.

Safety analysis set: all randomized participants who received at least 1 dose of treatment. One participant randomized to the placebo group received apremilast and was therefore allocated to the apremilast group for the safety analysis.