Five earlier papers on genetic effects on the P3 amplitude in adolescents, a quantity closely related to theta ERO power (Jones et al., 2006a; Andrew and Fein, 2010), used non-genotypic ACE models applied to twins (Katsanis et al., 1997; van Beijsterveldt et al., 1998; Anokhin et al., 2001; van Beijsterveldt et al., 2001; Carlson and Iacono, 2006). All found some degree of genetic effect on P3 amplitude in some or all of the sample groups studied, with heritabilities from the ACE models ranging from 33% to 79%. The studies of Katsanis et al. (1997) and Carlson and Iacono (2006) included only male twins. The studies of van Beijsterveldt et al. (1998, 2001) and Anokhin et al. (2001) included both male and female twins; genetic effects were confirmed only for males. The study by Carlson and Iacono (2006), using a slope-intercept latent growth model for phenotypic data, found both slopes and intercepts to be heritable in the age range from 17 to 23. This result is consistent with those presented here. A genotypic effect beginning at age 17 and continuing past
