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Child spacing and birth order: effect on intellectual ability in two-child families
Science (New York, N.Y.)
|December 1, 1978
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.