title: Genetic and environmental contributions to stability and change in children's internalizing and externalizing problems.
abstract: OBJECTIVE
  To estimate genetic, shared environmental, and nonshared environmental contributions to stability and change in internalizing and externalizing problems.
  
  
  METHODS
  Maternal Child Behavior Checklist ratings were obtained for 3,873 twin pairs at age 3 and 1,924 twin pairs at age 7. For 1,575 twin pairs, ratings were available at both ages.
  
  
  RESULTS
  For Internalizing/Externalizing ratings, genetic, shared, and nonshared environmental factors explained about 59/51%, 10/30%, and 31/19% of the variance at age 3, and 40/52%, 31/32%, and 29/16% of the variance at age 7. The phenotypic correlation of r = 0.38/0.54 between problems assessed at 3 and 7 years of age was explained for 66/55% by genetic factors, for 23/37% by shared environmental factors, and for 11/8% by nonshared environmental factors. The genetic, shared environmental, and nonshared environmental correlations between ages 3 and 7 were 0.51/0.57, 0.47/0.66, and 0.13/0.24, respectively.
  
  
  CONCLUSIONS
  Genetic and shared environmental factors were most important for the stability of Internalizing and Externalizing Problems between ages 3 and 7. Nonshared environmental factors were mainly age-specific. For Internalizing Problems, shared environment may become more important from early to middle childhood.
authors.affiliation: Department of Biological Psychology, Vrije Universiteit, Van der Boechorststraat 1, 1081 BT, Amsterdam, The Netherlands. Jolande@bhp.be
authors.forename: Jolande C
authors.initials: JC
authors.lastname: van der Valk
authors.forename: Edwin J C G
authors.initials: EJ
authors.lastname: van den Oord
authors.forename: Frank C
authors.initials: FC
authors.lastname: Verhulst
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
mesh_terms: D002648:Child; D002653:Child Behavior Disorders / Q000235:genetics* / Q000523:psychology*; D002675:Child, Preschool; D004777:Environment; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors; D013694:Temperament