Birth Order and Personality : a Within-family Test of Cultural Love

Abstract

Assumptions about the effects of birth order on personality abound in popular culture, self-help books, and the scholarly clinical literature. Although between family designs have consistently failed to find effects of birth order, a modified within-family design has documented predicted effects. That is, when one sibling compares him/herself to their siblings, birth order predicts who is nominated as the most conscientious and who is most open or rebellious (unconventional). However, directly comparing oneself to one's sibling encourages contrast effects. The purpose of this study was to employ a true within-family design that uses independent self-report data from both a firstborn and laterborn adult sibling from each family (in addition to parent reports of both siblings). In accord with Judith Rice Harris' theory of personality development, it was expected that neither adult siblings' independent self-reported personality traits nor parents' reports of those siblings' personality traits would differ by birth order.