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. 2. Objective of the present study is to conduct an 8-week double- blind, randomized, placebo-controlled trial to test the efficacy of pioglitazone in the treatment of bipolar depression. Outpatients are randomized to pioglitazone (15-45 mg/day) or placebo. We want to ensure the power of 80% to detect differential slopes that result in a moderate effect size (ES=0.55) on the primary outcome of IDS-C30 at 5% significance level. How many subjects would be required in each group