A Phase III, Multicenter, Randomized, Double-blind, Placebo-controlled, Dose-ranging Study to Evaluate the Efficacy and Safety of Xolair® (Omalizumab) in Patients With Chronic Idiopathic Urticaria (CIU)/Chronic Spontaneous Urticaria (CSU) Who Remain Symptomatic Despite Antihistamine Treatment (H1)

Type I Error Rate Control Plan Primary Outcome Measure In order to maintain an overall type I error rate of 0.05 (2-sided) across the 3 omalizumab dose levels, the testing of the primary Outcome Measure was conducted in the following hierarchical order. A p-value < 0.05 is only considered statistically significant if statistical significance was claimed at the previous stage. * Stage 1: Omalizumab 300-mg group vs. placebo * Stage 2: Omalizumab 150-mg group vs. placebo * Stage 3: Omalizumab 75-mg group vs. placebo Secondary Outcome Measures A hierarchical analysis of the following secondary Outcome Measures was performed for each dose found to be significant in the primary Outcome Measure. A p-value < 0.05 is only considered statistically significant if statistical significance was claimed at the previous stage. * Stage 1: Change from baseline to Week 12 in the urticaria activity score over 7 days (UAS7) * Stage 2: Change from Baseline to Week 12 in the weekly number of hives score * Stage 3: Time to minimally important difference (MID) response in the weekly itch severity score by Week 12 * Stage 4: Percentage of participants with a UAS7 score ≤ 6 at Week 12 * Stage 5: Percentage of weekly itch severity score MID responders at Week 12 * Stage 6: Change from Baseline to Week 12 in the weekly size of the largest hive score * Stage 7: Change from Baseline in the overall dermatology life quality index (DLQI) score at Week 12 * Stage 8: Change from Baseline in the overall dermatology life quality index (DLQI) score at Week 12 * Stage 9: Percentage of complete responders (UAS7 = 0) at Week 12