It is important to note that the sample included siblings from the same nuclear family. Adolescents within a given family cannot be treated as independent observations since siblings are nested within families. Adolescents within one family are likely to share characteristics (e.g., family SES, socialization, genotypes, etc.) and be more similar to each other compared to adolescents from a different family (Raudenbush and Bryk 2001; Jenkins et al. 2003). That is, it is likely that there is less variation between children from the same family in their delinquent behaviors than between adolescents from different families. Additionally, siblings share about 50% of their DNA sequence. Ignoring the nested multilevel structure of the data can bias results and lead to incorrect inferences given attenuated standard errors (Raudenbush and Bryk 2001).
