This document summarizes research supporting Alfred Alder's birth order theory of personality characteristics. Studies found firstborns were more responsible and successful, while later borns were more rebellious and outgoing. The current study also found support, with firstborns seen as most conscientious and achieving, and later borns as most liberal and rebellious. However, the study sample was small and uneven, limiting generalizability. Improved measures could better distinguish middle child traits as well.