2 shows the mean amplitude of the novelty P3 and target P3 for depressed patients and controls at midline sites. At the parietal site, where the target P3 was maximum, patients had significantly smaller novelty P3 than controls (t = 2.68, df = 38, P = 0.01) with an effect size of 0.85. There was also a nonsignificant trend for smaller target P3 in patients at the parietal site (t = 1.89, df = 38, P = 0.067) with an effect size of 0.60. The above results remained the same when the two patients having a comorbid anxiety disorder were excluded from the analyses. Thus, the overall ANOVA of amplitude in the P3 window yielded a main effect of Group (F = 6.36, df = 1,36, P = 0.016) and a significant Group by Stimulus interaction (F = 3.32, df = 2,72, P = 0.047).
