Group comparisons based on the principal component values are depicted in Figure 3. The reader should recall that the factor scores (P300 amplitude principal component values) can be negative because these values were standardized. Overall MANCOVA of schizophrenic patients, siblings, and controls for the temporoparietal and frontal P300 amplitude principal components resulted in a significant main effect of diagnosis (Rao R4,514 = 3.94; P = .004) (Figure 3) and sex (Rao R2,257 = 11.16; P<.001). No significant diagnosis × sex interaction was seen (Rao R4,514 = 0.86; P = .49). The significance level increased when including the control group and randomly selecting only 2 individuals from each family (1 index patient and 1 clinically unaffected sibling): we observed a significant main effect of diagnosis (Rao R4,388 = 3.84; P = .005), a significant main effect of sex (Rao R2,194 = 9.04; P<.001), and, again, no significant interaction (Rao R4,388 = 0.86; P = .49). Finally, the MANCOVA of schizophrenic patients with diagnostic subtype (paranoid, undifferentiated) and sex as independent factors showed a significant effect of diagnosis (Rao R2,57 = 5.24; P = .008) and sex (Rao R2,57 = 6.23, P = .004) but no significant interaction (Rao R2,57 = 2.03; P = .14). An equivalent MANCOVA of siblings with the 2 subgroups (nonpsychotic, psychiatric lifetime diagnosis[DSM-IV Axis I and II] present vs not present) revealed no significant main effect of subgroup (Rao R2,100 = 1.80; P = .17) or sex (Rao R2,100 = 0.68; P = .51) and no interaction (Rao R2,100 = 1.05; P = .35). The MANCOVA of patients with neuroleptic drug treatment vs no medication showed no significant main effects of medication use (Rao R2,56 = 0.36; P = .70) or sex (Rao R2,56 = 2.03; P = .14) and no interaction (Rao R2,56 = 1.05; P = .86). Likewise, schizo phrenic patients with and without a family history of schizophrenia did not show significantly different P300 amplitude principal component values (Rao R2,54 = 1.72; P = .19), although a statistical trend interaction with sex was observed (Rao R2,54 = 2.96; P = .06).