Birth Order

Birth order theories enjoy popular appeal because they provide an intuitive and commonsense explanation for the personality differences between siblings of different birth ranks. Additionally, the publication of popular resources, such as Kevin Leman's Birth Order Book (1985), that attribute myriad individual differences to birth order can create the impression that birth order plays a very significant role in personality development.

From 1976 to the end of the twentieth century researchers conducted more than 141 studies of the relationship between birth order and personality. The methodologically sound studies among this number generally have revealed few reliable differences in personality variables due to birth order Research suggests that siblings' roles in families depend more on gender, differing ages, and other variables than on actual birth order. DEAN CONGER/CORBIS (Dunn and Plomin 1990; Ernst and Angst 1983; Jefferson, Herbst, and McCrae 1998; Parker 1998; Phillips 1998; Stewart, Stewart, and Campbell 2001).

Frank Sulloway's book Born to Rebel (1996) generated renewed interest in birth order and personality research by contending that firstborn children are more responsible, competitive, and conventional, while laterborns are more playful, cooperative, and rebellious. Although Sulloway's rationale of niche-picking within the family is compelling, the hypothesized relationships have received only marginal support using the big-five model of personality, which comprises the traits of neuroticism, extraversion, openness, agreeableness, and conscientiousness (Jefferson et al. 1998). Within-family studies have yielded slightly more support for Sulloway's theory (Paulhus, Trapnell, and Chen 1999). Overall, studies of the relationship between birth order and personality have yielded very small effect sizes at best. Consequently, one can question whether birth order and personality effects either are noticeable in everyday life or possess significance for clinical practice. It is likely that birth order and personality effects are more apparent than they are real.