Bolded numbers along the diagonal are correlations between firstborns and secondborns.
By contrast, we found no firstborn-secondborn differences in observations of child speech or in standardized testing of children.
Vocabulary competence in firstborns and secondborns was only weakly related.
Parent-child interaction would account for the similarity between only and firstborn children in intellectual outcome.
These three-groups of firstborn attributes were relatively independent; for instance, even the first-born with less ability at schoolwork were given more responsibility at school.
About birth order and child vocabulary, this study shows an advantage for firstborns by maternal report, but not in observed production or by standardized testing.
Six of the children were firstborns and 10 were later borns.
Nineteen preterm infants (45%) and 17 full-term infants (41%) were firstborn.
