title: Intellectual similarity of virtual twin pairs: Developmental trends.
abstract: Virtual twins (VTs) are same-age unrelated siblings reared together from infancy who replicate twinship, but without the genetic relatedness. A 2005 report from the ongoing Fullerton Virtual Twin Study found an IQ intraclass correlation of .26 (p < .01, n = 113 pairs) and a within-pair difference of 13.22 IQ points. The average age of VTs in that study was 8.10 years (SD = 8.56, range: 4.01-54.84 years). An opportunity to retest members of 43 VT pairs, 1.70-8.96 years after their time 1 assessment, allowed additional analyses of genetic and environmental influences underlying general intellectual development. A decrease in the VT IQ correlation and an increase in the within-pair difference were indicated, consistent with increasing genetic and/or non-shared environmental influences and decreasing shared environmental influence on general intellectual development throughout childhood.
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Segal
authors.forename: Shirley A
authors.initials: SA
authors.lastname: McGuire
authors.forename: June
authors.initials: J
authors.lastname: Havlena
authors.forename: Patricia
authors.initials: P
authors.lastname: Gill
authors.forename: Scott L
authors.initials: SL
authors.lastname: Hershberger