Confirming the etiology of adolescent acting-out behaviors: an examination of observer-ratings in a sample of adoptive and biological siblings.

A recent meta-analysis revealed the presence of moderate shared environmental influences (C; or those familial and contextual experiences that increase sibling similarity regardless of the proportion of genes shared) on most forms of child and adolescent psychopathology (Burt, 2009), including antisocial behavior. This finding was somewhat surprising, as prior theory held that meaningful environmental influences were primarily non-shared or child-specific in nature (Plomin & Daniels, 1987). Burt (2009) also examined a number of potential moderators of these effects, including informant. C effects were identified for multiple individual informant-reports, thereby bolstering conclusions regarding the importance of these effects. Even so, behavioral genetic research on psychopathology to date (and thus, the research included in the meta-analysis) has relied almost exclusively on individual informant-reports (and particularly parent and child reports), each of which are subject to various sources of rater bias (as reviewed in Burt, 2009; De Los Reyes & Kazdin, 2005). Depending on the child's age, his or her self-report may be relatively unreliable, thereby serving to reduce twin correlations and artifactually increasing estimates of the non-shared environment (as seen in Burt, 2009). Alternately, parents may have limited knowledge regarding normative child behavior, and thus may interpret specific behaviors as more or less pathological accordingly. Parents may also over- or under-estimate the similarity of their twins (referred to as “sibling contrast”), thereby artifactually inflating heritability estimates. Teachers, by contrast, have extensive knowledge of normative child behavior, although this knowledge is largely context-specific. Moreover, all informant-reports may be influenced by recency effects or by the rater's own personality/psychological background. For example, a parent may report that a child acts out more or less than he/she objectively does based on the parent's own psychological state, or based on a recent incident. In short, results obtained through particular individual informant-reports are somewhat less conclusive than one would like. Some researchers have attempted to circumvent reliance on individual imformant-reports with the use of informant composites, in which multiple informant-reports are combined prior to analysis. This procedure has been found to improve the validity of the assessment (Kraemer et al., 2003). However, because it is difficult to tease apart error and true score variance even when combining informants, this solution is unlikely to fully ameliorate issues of potential rater bias. Observer-ratings of children's behaviors offer another compelling strategy for avoiding most forms of rater bias. As with teacher-reports, children are rated in comparison to other children in the same developmental stage, thereby ensuring that children are evaluated in reference to normative child behaviors. Coders also receive extensive manual-based training to reach and then maintain reliability with other coders. Scores obtained this way thus allow researchers to obtain data that are largely (though, of course, not entirely) free of personological interference. Given these two clear advantages, we would thus argue that the use of observer reports can meaningfully supplement our understanding of the etiology of adolescent antisocial behavior. To date, there are several twin studies examining etiological influences on observer-ratings of acting-out behaviors (Arsenault et al., 2003; Deater-Deckard, 2000; Leve, Winebarger, Fagot, Reid, & Goldsmith, 1998; Marceau et al., submitted; O'Connor, Hetherington, Reiss, & Plomin, 1995; Plomin, Foch, & Rowe, 1981). Early work by Plomin et al. (1981), Leve et al. (1998), and Deater-Deckard (2000) estimated shared environmental influences on observer-ratings to be moderate-to-large in magnitude (25-42%). These findings were largely replicated in more recent work by Marceau et al. (submitted), who examined the etiology of observer-ratings in three independent samples. Estimates of C were prominent across all three samples (i.e., 44%, 77%, and 38%). Indeed, only two existing studies (Arsenault et al., 2003; O'Connor et al., 1995), to our knowledge, have not found evidence of significant shared environmental influences, although in both cases, the C effect was estimated to be “non-zero” (10-12%). As there are no consistent differences in twin age, twin sex, or the severity of the coded behaviors, it remains unclear what may account for these differences across studies. Even so, it is noteworthy that C was uniformly estimated to be non-zero across all studies, and was typically moderate-to-large in magnitude. Given this, we would argue that the above studies collectively support the presence of C on observer-ratings, and in this way, argue against the notion that shared environmental influences on antisocial behavior are primarily a function of rater bias. Even so, additional research is needed to confirm this conclusion. First, available studies have exclusively examined twin/twin-sibling samples, which are not particularly well suited for examining the shared environment. In particular, C can be confounded by passive gene-environment correlations (i.e., passive rGE) when the origins are in fact a function of common parent-child genes. Simply put, the environment provided to one's biological children (including parental behavior towards the child) reflects the genetically influenced preferences and tendencies of the parent. And because parents share genes with their biological children, the child's genes are then correlated with his/her parent's behavior. Fortunately, the role of passive rGE in C can be circumvented by examining adoptive siblings. Because adoptive siblings do not share genes with their adoptive family members, passive rGE are entirely eliminated, providing a “direct” estimate of C. It would thus be critically important to extend the above findings to a sample of adoptive siblings, thereby firmly ruling out passive rGE as an explanation for prior results. Second, informant-specific shared environmental influences have often been interpreted as suggestive of rater bias (Bartels et al., 2004) rather than other, more meaningful possibilities (e.g., situational specificity). This attribution may reflect the fact that shared environmental effects have historically been thought to have a minimal influence on outcome (Plomin & Daniels, 1987). Regardless of the reason, because of this history, it is important to confirm that shared environmental effects are not confined to particular informants. Shared environmental influences that overlap with those on observer-ratings would constitute particularly strong evidence for persistence across informants, given both the very different assessment strategies (e.g., lifetime assessment versus a 10-minute slice of observation) as well as the fact that observer-ratings should be largely free from rater bias. Should shared environmental influences on observer-ratings overlap with those on other informant-reports, it would provide convincing evidence against rater bias as a primary explanation for observed shared environmental influences. The current study sought to fill these gaps in the literature, so as to more definitely support or refute claims of meaningful C on adolescent antisocial behavior. To do so, we examined the sources of etiological influence on observer-ratings of acting-out behaviors, as well as the origins of overlap between these ratings and parent- and child-reports, in a sample of adoptive and biological siblings. Should there be evidence of significant C on observer-ratings and evidence of shared environmental overlap with the other informants (as we expected), the results would provide compelling support for prior claims that shared environmental influences constitute a meaningful source of variance within adolescent antisocial behavior.