The phenotypic correlation between maltreatment and conduct problems was small but statistically significant (r = 0.15, p < 0.05). Table 3 shows cross-sibling within-trait and cross-trait correlations by gender and sibling type. Since MZ twins are more similar genetically than DZ twins and full siblings, greater cross-sibling correlations between MZ twins than between DZ twins and full siblings suggest genetic influence. Therefore, Table 3 suggests that children’s genes exert only a small influence on the maltreatment they report. Shared environmental influences are also suggested, as the DZ correlation is greater than half the MZ correlation. The MZ and DZ correlations are greater than the full sibling (FS) correlations, which is not surprising given that twins are the same age but FS are not, suggesting a role of the twin-specific environment. Most of the variance in maltreatment appears to be due to nonshared environmental influences, as the correlations for MZ twins, who share 100% of their genes and the shared environment, are well below one. Detailed behavior genetic decompositions of each form of maltreatment (i.e. physical maltreatment, neglect, and sexual maltreatment) are presented elsewhere (Schulz-Heik et al. 2009).
