title: The genetic and environmental etiologies of individual differences in early reading growth in Australia, the United States, and Scandinavia.
abstract: This first cross-country twin study of individual differences in reading growth from post-kindergarten to post-second grade analyzed data from 487 twin pairs from the United States, 267 twin pairs from Australia, and 280 twin pairs from Scandinavia. Data from two reading measures were fit to biometric latent growth models. Individual differences for the reading measures at post-kindergarten in the United States and Australia were due primarily to genetic influences and to both genetic and shared environmental influences in Scandinavia. In contrast, individual differences in growth generally had large genetic influences in all countries. These results suggest that genetic influences are largely responsible for individual differences in early reading development. In addition, the timing of the start of formal literacy instruction may affect the etiology of individual differences in early reading development but have only limited influence on the etiology of individual differences in growth.
authors.affiliation: Department of Psychology and Neuroscience, University of Colorado Boulder, Boulder, CO 80309, USA. micaela.christopher@colorado.edu
authors.forename: Micaela E
authors.initials: ME
authors.lastname: Christopher
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Hulslander
authors.forename: Brian
authors.initials: B
authors.lastname: Byrne
authors.forename: Stefan
authors.initials: S
authors.lastname: Samuelsson
authors.forename: Janice M
authors.initials: JM
authors.lastname: Keenan
authors.forename: Bruce
authors.initials: B
authors.lastname: Pennington
authors.forename: John C
authors.initials: JC
authors.lastname: Defries
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Wadsworth
authors.forename: Erik
authors.initials: E
authors.lastname: Willcutt
authors.forename: Richard K
authors.initials: RK
authors.lastname: Olson
mesh_terms: D001315:Australia; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007206:Individuality; D008297:Male; D011932:Reading; D012537:Scandinavian and Nordic Countries; D012931:Social Environment; D014429:Twins, Dizygotic / Q000523:psychology; D014430:Twins, Monozygotic / Q000523:psychology; D014481:United States