title: Intelligence, birth order, and family size.
abstract: The analysis of the National Child Development Study in the United Kingdom (n = 17,419) replicates some earlier findings and shows that genuine within-family data are not necessary to make the apparent birth-order effect on intelligence disappear. Birth order is not associated with intelligence in between-family data once the number of siblings is statistically controlled. The analyses support the admixture hypothesis, which avers that the apparent birth-order effect on intelligence is an artifact of family size, and cast doubt on the confluence and resource dilution models, both of which claim that birth order has a causal influence on children's cognitive development. The analyses suggest that birth order has no genuine causal effect on general intelligence.
authors.affiliation: London School of Economics and Political Science, United Kingdom. S.Kanazawa@lse.ac.uk
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kanazawa
mesh_terms: D000293:Adolescent; D001722:Birth Order; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D005190:Family; D005260:Female; D006801:Humans; D007360:Intelligence; D008297:Male; D008962:Models, Theoretical; D011446:Prospective Studies; D035781:Siblings; D012959:Socioeconomic Factors; D006113:United Kingdom