1. Objectifs

Intentions :
«[T]he first goal of the present study was to examine whether one twin’s proactive aggression predicted changes in the other twin’s proactive aggression, and whether one twin’s reactive aggression predicted changes in the other twin’s reactive aggression. […] The second goal of this study was to examine whether parental expressions of coercion and hostility moderate
over time associations between one twin’s reactive or proactive aggression and changes in the other twin’s reactive or proactive aggression.» (p. 456-457)

2. Méthode

Échantillon/Matériau :
«Participants consisted of 452 same-sex twins (113 male dyads, 113 female dyads) drawn from an ongoing longitudinal study (Quebec Newborn Twin Study) of a population-based sample of twins from the greater Montreal area who were recruited at birth between November 1995 and July 1998 (Boivin et al., 2013). Participants were limited to dyads in which both siblings experienced similar levels of parental treatment. The sample consisted of 137 monozygotic and 89 same-sex dizygotic twin pairs enrolled in kindergarten». (p. 457)

Instruments :
- Reactive aggression and proactive aggression
- Parental Cognitions and Conduct

Type de traitement des données :
Analyse statistique

3. Résumé

«We found contagion effects for both proactive and reactive aggression, such that twins of more proactively aggressive children become more proactively aggressive and twins of more reactively aggressive children become more reactively aggressive. […] We found that early reactive aggression predicted changes in proactive aggression, such that twins who are initially more reactively aggressive become more proactively aggressive over time. […] We found that contagion between twins in both reactive aggression and proactive aggression was moderated by parental coercion, such that only twins whose parents were relatively high in coercion-hostility exhibited contagion. First, higher levels of proactive aggression in one twin gave rise to greater increases in proactive aggression in the other twin. Interestingly, similar twin contagion effects were also found for reactive aggression. Second, reactive aggression manifested by each twin fed their tendency to use proactive aggression but not the other way around. Finally, and new to this study, is the finding that the strength of across-twin influence, but not within-twin influence, differs as a function of parental coercion-hostility. Specifically, aggression begets aggression for twins with parents relatively high on coercion-hostility but not for twins with parents who are relatively low or moderate on coercion-hostility.» (p. 461)