A mixed-model analysis of covariance (ANCOVA) comparing the log10-EEG power and gender between groups at electrode sites Fz, Cz, and Pz, with age as a covariate, indicated a main effect of group (F=4.05, df=2, 47, p<0.03), a group-by-gender interaction (F=3.77, df=2, 47, p=0.03), and a group-by-frequency interaction (F=2.04, df=14, 336, p<0.02). Age was not a significant covariate (t=0.07, df=47, p=0.95). To investigate group differences further, additional analyses of variance (ANOVAs) were conducted between two groups only. The patients with schizophrenia or schizoaffective disorder showed reduced power across all frequencies of stimulation, as indicated by a main effect of group (F=5.26, df=1, 41, p<0.03), with no interactions. An ANOVA between the subjects with schizotypal personality disorder and the subjects with schizophrenia or schizoaffective disorder revealed a main effect of group (F=5.13, df=1, 30, p<0.04) and a group-by-frequency interaction (F=3.13, df=7, 210, p=0.004) (F1).
In an effort to determine whether the group differences were obtained as a result of differences in resting EEG unrelated to stimulus frequency, a mixed-model ANCOVA comparing the log10-EEG power and the gender of the subjects with nonstimulated frequencies with age as a covariate was computed. Analyses revealed no main effect of group or interactions involving group factors, indicating that EEG power at nonstimulated frequencies did not differ between groups (F1).
A mixed-model ANOVA measuring N100 amplitude indicated no significant differences between groups (F=1.32, df=2, 51, p=0.28), no group-by-frequency interaction (F=0.36, df=6, 153, p=0.91), and no group-by-site interaction (F=0.95, df=4, 102, p=0.44).