title: Twins: within-pair similarity on Bayley's Infant Behavior Record.
abstract: Summary scores for behaviors rated on Bayley's Infant Behavior Record were obtained by summing sequential ratings for same-sex twins participating in a longitudinal study. The first year scores were based on visits made at 3, 6, 9, and 12 months, by 55 identical and 27 fraternal pairs; the second year scores were based on visits at 18, 24, and 30 months, by 47 identical and 27 fraternal pairs. During the first year, within-pair correlations for almost all behaviors were stronger for identical than for fraternal pairs; in the second year, within-pair correlations for identical twins were similar to those of fraternal twins except for the more cognitive behaviors. Composite scores were calculated for two behavioral clusters--one composed of behaviors related to Primary Cognition, and the other composed of behaviors related to Extraversion. Within-pair correlations were higher for identical than for fraternal twins in both the first and second years, indicating stronger and more consistent genetic influences on the more cognitive behaviors.
mesh_terms: D000367:Age Factors; D001007:Anxiety; D002652:Child Behavior; D002675:Child, Preschool; D003071:Cognition; D005120:Extraversion, Psychological; D005239:Fear; D005260:Female; D005824:Genetics, Behavioral; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity; D009048:Motor Skills; D009769:Object Attachment; D011247:Pregnancy; D011581:Psychological Tests; D012737:Sex Factors; D012919:Social Behavior; D013694:Temperament; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic