Birth order differences in normal personality traits: Perspectives from within and outside the family

► Birth order hypotheses of Sulloway (1996) were tested with a between-families design. ► Few studies of birth order have used informants, such as family members or peers. ► Personality ratings were gathered from the self, a peer, and one parent. ► No significant differences between firstborns and laterborns on five factor traits. ► Effect sizes were near-zero using self-ratings and ratings by peers and parents.