title: Child spacing and birth order: effect on intellectual ability in two-child families.
abstract: The effect on intellectual ability of the spacing of the birth of siblings was studied in two series of young men from two-child families: (i) 535 pairs of brothers and (ii) 1511 unrelated firstborn and secondborn. Birth-order effect and level of ability were not influenced by length of interval between firstborn and secondborn.
mesh_terms: D001722:Birth Order; D005190:Family; D005260:Female; D006801:Humans; D007360:Intelligence; D008297:Male; D008423:Maternal Age; D012959:Socioeconomic Factors; D013997:Time Factors