title: A monozygotic twin difference study of friends' aggression and children's adjustment problems.
abstract: This study used the monozygotic (MZ) twin difference method to examine whether differences in friends' aggression increased the differences in MZ twins' aggression and depressive symptoms from kindergarten to Grade 1 and whether perceived victimization by the friend played a mediating role in this context. Participants were 223 MZ twin pairs. Results showed that differences in kindergarten friends' aggression significantly predicted an increased difference in MZ twins' aggression from kindergarten (mean age = 6.7 years) to Grade 1 (mean age = 7.5 years) for both boys and girls. Differences in perceived victimization by the friend mediated this association, albeit only in boys. Differences in perceived victimization by the friend also predicted an increase in MZ twins' differences in depressive symptoms. These results support the importance of friendship experiences during early childhood.
authors.affiliation: University of Montreal, Montreal, QC, Canada. frank.vitaro@umontreal.ca
authors.forename: Frank
authors.initials: F
authors.lastname: Vitaro
authors.forename: Mara
authors.initials: M
authors.lastname: Brendgen
authors.forename: Michel
authors.initials: M
authors.lastname: Boivin
authors.forename: Stéphane
authors.initials: S
authors.lastname: Cantin
authors.forename: Ginette
authors.initials: G
authors.lastname: Dionne
authors.forename: Richard E
authors.initials: RE
authors.lastname: Tremblay
authors.forename: Alain
authors.initials: A
authors.lastname: Girard
authors.forename: Daniel
authors.initials: D
authors.lastname: Pérusse
mesh_terms: D000374:Aggression / Q000523:psychology*; D002648:Child; D002652:Child Behavior / Q000523:psychology*; D002675:Child, Preschool; D019548:Crime Victims / Q000523:psychology*; D003863:Depression / Q000523:psychology*; D005260:Female; D033062:Friends / Q000523:psychology*; D006801:Humans; D008297:Male; D012917:Social Adjustment; D012931:Social Environment; D012938:Social Perception; D014430:Twins, Monozygotic / Q000523:psychology*