The development of children's problem behaviors: A twin-singlton comparison and the influence of parental divorce Robbers, S.C.C. 2012-04-19 Doctoral Thesis

Twin-family studies have largely contributed to our understanding of the etiology of behavioral and emotional problems in childhood. From these studies we learned that almost every behavioral or psychological trait is ‘heritable’ to some extent. We also learned that both nature and nurture play important roles in the etiology of behavioral and emotional problems, and that these factors may act independently of one another as well as interactively (i.e., gene-environment interplay). Moreover, twin studies have given insight into the important distinction between environmental factors shared by siblings (e.g., parental socio-economic status) and those not shared by siblings (e.g., peer groups) (Boomsma, Busjahn, & Peltonen, 2002; Hudziak & Faraone, 2010). An important assumption that is made when using twin data is that results from twin samples can be generalized to singleton populations. However, the validity of this assumption needs to be examined.
http://repub.eur.nl/res/pub/32164/120418_Robbers%2C%20Sylvana%20Cornelia%20Catharina.pdf