Birth order and the dominance aspect of extraversion: Are firstborns more extraverted, in the sense of being dominant, than laterborns?

The present study set out to examine the relationship between birth order and the dominance facet of extraversion in a community sample of around 1500 participants. In contrast, to Sulloway’s (1995) predictions, the present study, using a between-family design, found firstborns to be less extraverted, in the sense of being less dominant, than laterborns. This effect was found while controlling for potential confounds, such as age, and using a constant sibship size. Results are discussed with reference to the current literature on birth order and personality.