S100B and major depressive disorder: As illustrated in Figure 1, serum S100B reached high effect sizes in both MDD (3.0 ± 1.03) and BD (1.4 ± 0.44; T = 5.82, = 6.4, df = 3, = 3, P = .01, = .008; 2-tailed one-sample Student's t-test against 0).