Sex Differences in the Impact of the Number of Older and Younger Siblings on IQ Performance

Abstract

The authors present evidence that reassesses a recent hypothesis put forth by Paulhus and Shaffer (1981), that females are less likely than males to show decrements in intellectual growth normally associated with larger number of siblings. Using data from a large, nationally representative sample of children, our results contradict this hypothesis. Our data reveal that females are slightly less likely than males to show declines in verbal IQ performance as the number of siblings increases, but are more likely than males to show declines in nonverbal IQ performance as the number of siblings increases. In addition, our analysis suggests that the negative impact of the number of siblings on test performance increases with age under some conditions. The discrepancies between the Paulhus and Shaffer (1981) study and our own are then discussed.