Intelligence,Birth Order,and Family Size

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. © 2012 by the society for personality and social psychology,inc.