The correlation between the two siblings on the latent externalizing factor was large for MZ twins (r = 0.79, 95% CI = 0.73-0.84), while the correlation was medium to large for DZ twins and non-twin biological siblings (r = 0.45, 95% CI = 0.36-0.55), and smaller but statistically significant for adoptive siblings (r = 0.21, 95% CI = 0.09-0.33). The adoptive sibling correlation is a direct estimate of shared environmental influences, indicating that sibling similarity was due to a combination of genetic and shared environmental influences.
