BIRTH ORDER AND INTELLIGENCE.

The article focuses on the effect of birth order on intelligence. Some studies have indicated a superiority in intelligence of later born over firstborn, while other studies have suggested that firstborn are superior in intelligence to those of later ordinal positions. Differences in intelligence do not appear significantly large enough to account for the observed large differences in achievement among the ordinal positions reported in numerous studies, and economic hypotheses likewise fail to explain the differential achievement by birth order. Further research on birth order, therefore, may be more fruitful if focused on some of the social-psychological variables reported to be associated with ordinal rank. The findings reported herein for two, three, four and five-child families point toward a slight superiority in intelligence of firstborn over last born, with a tendency for intermediate born to have intelligence scores between their older and younger siblings. However, while these differences between firstborn and last born are statistically significant in a majority of the cases, the mean difference in the standardized intelligence scores between firstborn and last born is 1.64, comparable to 3.28 IQ points. Such a small difference is unlikely to have any practical effects on the achievement of firstborn relative to that of last born.