Another important limitation in the existing research is the lack of research directly comparing important subgroups of children with CD and ODD. For example, a number of studies across various countries have supported the distinction between childhood- and adolescent-onset forms of CD [58, 59]. Recent evidence suggests that children who show significant levels of callous and unemotional (CU) traits (i.e., lacking empathy and guilt; constricted emotions) are also an important subgroup in that they tend to show a more severe form of CD that seems to be more persistent and associated with violence and offenses ([36, 38] for reviews). However, the vast majority of these studies on the importance of CU traits have been conducted in the US or Canada [36] with only a few studies carried out in Europe [28, 30, 31, 78] and Israel [73]. Clearly more cross-cultural research is needed on the importance of CU traits for designating an important subgroup of youth with CD.
