Final answer:
Studies on how birth order affects personality traits have not conclusively supported Adler's theory that birth order can shape personality. The primary challenge in such research is the inability to randomly assign birth order, making it challenging to eliminate confounding variables and establish causation in these studies.
Step-by-step explanation:
Large-scale studies on the effect of birth order on personality characteristics have garnered considerable interest within the field of psychology, particularly since Alfred Adler proposed his theory that an individual's position among siblings has significant effects on personality development. Adler argued that first-born children may become overachievers to compensate for the loss of attention with the arrival of a sibling, while the youngest might be spoiled and the middle child might be motivated to balance out the dynamic between the eldest and youngest. However, subsequent research has struggled to conclusively confirm these hypotheses with scientific data, indicating the complexity of the relationship between birth order and personality traits. One significant barrier in conducting birth order studies as a randomized experiment is that one cannot ethically or practically manipulate a person's birth order - it is a naturally occurring variable. Hence, studies on birth order and personality cannot use random assignment, a cornerstone of experimental research, which often leads to difficulty in controlling for various confounding variables. The lack of randomization makes it hard to establish causation.