Are you a firstborn who is neurotic? Or an emotionally stable middle child? Perhaps you're the youngest but the most ambitious? Researchers examine the idea that birth order affects personality
Settled: No systematic differences in personality by birth order of siblings. Study with data, N>20,000, from Germany, the U.K. and the U.S. They compared personality profiles of siblings but also of people with different birth orders who had never met.
Does Birth Order Affect Personality? via (tl;dr: no)
The importance attached to sibling position/birth order in determining personality has been exaggerated. Research suggests that any effects are quite small, the effects of sibling sequence may vary across families, and other factors play much bigger roles.
Beliefs in birth order and #Personality may be wrong says newer research