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Birth Order and Personality -- Not Again!
Suzanne M. Phillips
Gordon College
Paper presented to the annual meeting of the Eastern Psychological Association in Boston
Massachusetts in February, 1998
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Birth order has enjoyed a long history as an intuitively important variable in personality theory,
beginning with Adler’s (1927) introduction of the concept to explain sibling differences. However, efforts to
demonstrate the impact of birth order on personality have produced inconsistent results, and reviewers of
this literature have not detected clear effects. Schooler (1972) reviewed studies of normally and mentally
disordered subjects and concluded that birth order does not influence personality. Ernst and Angst (1983)
reviewed research published between 1946 and 1980, again with the conclusion that birth order is
unrelated to personality. Ernst and Angst (1983) also presented their own study, of over 7500 men and
women ages 19 and 20, in which personality and birth order were not related. So thoroughly unsupported
is the birth order--personality link, that when Plomin and Daniels (1987) discussed sibling differences in
personality, they dismissed birth order after a brief discussion.
Into this bleak setting, Sulloway (1996) published Born to Rebel: Birth Order, Family Dynamics,
and Creative Lives. In the book (and in a 1995 article), Sulloway returns to the extensive literature review
published by Ernst and Angst in 1983. He gleans apparently better-controlled studies and organizes
them using the “big five” factorial model of personality proposed by Costa and McCrae (1987). Sulloway
finds differences between firstborns and laterborns on all five dimensions, with no distinction between
different laterborn positions. Specifically, Sulloway finds that firstborns are more extraverted , neurotic,
and conscientious, and laterborns are more agreeable and open to experience. Sulloway estimates the
birth order effect for each personality dimension (positive correlations indicate that firstborns score
higher): extraversion (.10); neuroticism (.20); conscientiousness (.35); agreeableness
(-.30); and openness to experience (-.40; Sulloway, 1995).
Sulloway’s work suggests that the dimensional conceptualization of personality will clarify birth
order research. Looking through “big five” lenses, researchers might find the birth order--personality
connections that seem present to intuition. Sulloway’s claims invite a birth order study using a current big
five personality measure. Such a study is reported herein.
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Method
A total of 196 introduction to psychology students at a mid-sized college campus completed the
NEO-PI-R, Costa and McCrae’s (1987) highly reliable and valid measure of the five major personality
dimensions used by Sulloway. Subjects also described their families, including the ages of family
members, the number of siblings, and whether the siblings were step-siblings or not. For the sake of
making the birth order data as “clean” as possible, subjects with step-siblings or deceased siblings were
excluded, leaving 177 people (87 men and 90 women) in the sample. On average, subjects were 20.3
years old, SD = 4.72. As Sulloway’s formulation suggests, the group was divided into firstborns, including
only children (n = 65), and laterborns (n = 112).
Results
None of the point-biserial correlations between birth order (firstborn/laterborn) and the five NEOPI-R personality dimensions was statistically significant: for extraversion, r (175) = .07; for neuroticism, r
(175) = .03; for conscientiousness, r (174) = -.12; for agreeableness, r (175) = .07; and for openness to
experience, r (175) = .06. Dividing laterborns into middle children and youngest children does not uncover
significant effects; neither does removing only children from the firstborn group. Each of the five
personality dimensions measured by the NEO-PI-R has six facet scales; of the 30 facet scales, only one
(C6) showed a statistically significant difference between firstborns and laterborns, but opposite the
direction predicted by Sulloway.
Sulloway (1995) raised concerns about the statistical power of previous work. At an alpha-level of
.05, the statistical tests presented here have ample power (.98 and greater) in reference to the
correlations hypothesized for conscientiousness, agreeableness, and openness to experience. The level
of power is moderate (.77) for the test of the neuroticism effect, and weak (.26) for the test of the
extraversion effect.
Sulloway (1996) also criticized previous research for comparing children across different family
sizes. In the present study, when family size is held constant, birth order position remains unrelated to the
five personality dimensions for families in which there were two children (n = 91) or three children (n =
43).
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Discussion
Twenty-five years ago, Schooler (1972) concluded that personality is not influenced by birth
order. The present study supports Schooler’s conclusion. Even so, psychologists and lay people both
seem drawn to birth order effects on personality. Many child development texts discuss how personality
varies by ordinal position (e.g., Bukatko & Daehler, 1996; Hetherington & Parke, 1993). When surveyed,
students report that they believe birth order effects on personality exist, and they agree about the typical
personality of various ordinal positions (Nyman, 1995). As a culture and as a profession, we believe that
personality varies with ordinal position, despite the conclusions of extensive reviews in the area.
This resilient belief may grow out of two observations of families which are supported by
research: siblings differ dramatically from one another in personality (Plomin & Daniels, 1987), and
parents treat children differently by ordinal position (Hoffman, 1995). If parenting influences personality,
then it would seem that some of the variation in siblings’ personalities should be accounted for by ordinal
position. These elements fit together neatly, and the reasoning seems sound, but the conclusion is wrong.
The present study, using a high quality and comprehensive five factor measure of personality and
designed with adequate statistical power, concurs with a long history of research in finding no birth order
effect on personality. Focusing on solving this puzzle would seem a fruitful avenue for future work.
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References
Adler, A. (1927). Understanding human nature. Garden City, NY: Garden City.
Bukatko, D., & Daehler, M. W. (1996). Child development: A thematic approach (2nd ed.).
Boston: Houghton Mifflin.
Costa, P. T., Jr., & McCrae, R. R. (1987). NEO-PI-R professional manual. Odessa, FL:
Psychological Assessment Resources.
Ernst, C., & Angst, J. (1983). Birth order: Its influence on personality. Berlin: Springer.
Hetherington, E. M., & Parke, R. D. (1993). Child psychology: A contemporary viewpoint (4th ed.).
NY: McGraw-Hill.
Hoffman, L. W. (1995). The influence of the family environment on personality: Accounting for
sibling differences. Psychological Bulletin, 110, 187-203.
Nyman, L. (1995). The identification of birth order personality attributes. Journal of Psychology,
129, 51-59.
Plomin, R., & Daniels, D. (1987). Why are children in the same family so different from one
another? Behavioral and Brain Sciences, 10, 1-16.
Schooler, C. (1972). Birth order effects: Not here, not now! Psychological Bulletin, 78, 161-175.
Sulloway, F. J. (1995). Birth order and evolutionary psychology: A meta-analytic overview.
Psychological Inquiry, 6, 75-80.
Sulloway, F. J. (1996). Born to rebel: Birth order, family dynamics, and creative lives. NY:
Pantheon.