Birth Order and Intelligence: is There a Correlation?
Sponsored by Missouri Western State University Sponsored by a grant from the National Science Foundation DUE-97-51113
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The proper APA Style reference for this manuscript is:
ROW, A. G. (2001). Birth Order and Intelligence: is There a Correlation?. National Undergraduate Research Clearinghouse, 4. Available online at Retrieved April 25, 2017 .

Birth Order and Intelligence: is There a Correlation?
Missouri Western State University DEPARTMENT OF PSYCHOLOGY

Sponsored by: Brian Cronk (
The effect of one`s birth order on his or her intelligence was investigated. 50 Missouri Western State College students participated. The students completed a short intelligence test. A one-way ANOVA was done to compare the intelligence level of only children, first-born children, middle children, and last-born children. The results indicated that only children and first-born children have a higher level of intelligence than middle and last- born children.

What is intelligence? Stephen Ceci (2001) says at the very least, intelligence can be defined as oneís ability for complex thinking and reasoning. Over the years there has been much debate about intelligence. How important is it really, how is it measured, and things of that nature. One thing that is for certain, there are many factors in oneís life that can mold his or her intelligence level. In a recent article (Ceci, 2001), it is stated that school attendance, whether or not one is breast-fed, and a personís head size are all positively correlated with intelligence. One surprising thing found in the article is that intelligence is not influenced by birth order. The author (Ceci, 2001) claims that birth order plays no part in oneís intelligence, that smart people tend to have smart families. This statement goes along with some literature on the subject, but there is much literature that argues for the correlation between birth order and intelligence level. Alfred Alder was one of the first researched to look at birth order and how it affected oneís personality. His theory looks at first-born children, middle children, last-born children, as well as only children. Adler theorized that an individualís birth order shapes his or her personality because of the different experiences that each birth order goes through (Engler, 1999). Adlerís theory on birth order, had implications for birth order and intelligence. Adler suggested that the oldest children tend to be more intelligent (Engler, 1999), but does this proposal really hold true? According to University ofOklahoma psychology professor Joseph Lee Rodgers, Ph.D., the theory does not hold any truth. Rodgers (2001) challenges popular belief by arguing that there is no immediate link between birth order and intelligence. He claims that studies that have found a correlation between birth order and intelligence were flawed because they did not compare children within families. Rodgers therefore evaluated data that was taken from within families using the 1979 National Longitudinal Survey of Youth. This survey is a consolidation of intelligence test scores taken twice a year from a group of children ages 14 to 21. By comparing scores within families, Rodgers came to the conclusion that there is no link between birth order and intelligence (Rodgers, 2000). Rodgers also argues against the Confluence Theory (Rodgers, 2000). The Confluence Theory states that the intelligence level in the family decreases as the number of children increases. The second part of the Confluence Theory claims that the reason for this decrease is due to the fact that the elder children teach the younger siblings. In other words, the older children gain intellectually from teaching their younger siblings, and because last born children have no one to teach, their development, in turn suffers. (Zajonc, Markus, Berbaum, Baugh, & Moreland, 1991). Rodgers argues that parents who are more educated and with carrer paths, often have fewer children because they tend to delay having children. He claims that intelligence is mostly influenced by genetics and the quality of child rearing. He goes on to say that, ďparenting efforts can make all the difference in a childís developmentĒ (Rodgers, 2000). It should be noted that some evidence suggests that only children perform slightly better than other children in regards to achievement intelligence. But that eldest children have the edge over the onlies due to the fact that they have the opportunity to teach their younger siblings (Pines, 1981). In a study by Terry (1989), it was found that of 79 prominent psychologists, 52 percent were first born or only children. Terry gathered that this may be due to the ďedgeĒ that the oldest children have academically. This edge, Terry states, permitís these children to undertake the doughty task of becoming a psychologist in the first place. Another study of the same kind found that first born children achieve a higher professional status than their siblings who are born later (Schachter, 1963). In a study by Terry (1989), it was found that of 79 prominent psychologists, 52 percent were first born or only children. Terry gathered that this may be due to the ďedgeĒ that the oldest children have academically. This edge, Terry states, permitís these children to undertake the doughty task of becoming a psychologist in the first place. Another study of the same kind found that first born children achieve a higher professional status than their siblings who are born later (Schachter, 1963). Previous literature, as listed above, argues for both sides to the debate of birth order and intelligence. This study proposes to investigate the following question: is there a correlation between one`s birth order and his or her intelligence?


There were 50 Missouri Western State College studnents that participated in the study. There were freshman, sophomore, junior, and senior participants. The partcipant`s ages ranged from 18 to 60. There were 10 only children, 11 first-born children, 16 middle children, and 13 last-born children.

Selected questions from the Classic Intelligence Test found on were taken and made into a 20 question test. A copy of this test may be found in the appendix.

Students found working in the library computer lab on the campus of Missouri Western State College were asked to participate. The participants completed the 20 question intelligence test and gave some general demographic information such as age and sex, as well as his or her respective birth postition. Upon completion of the test, the participants were debriefed.

The mean intelligence scores of the four birth positions were compared using a one-way ANOVA. A significant differnce was found (F(3, 46)= 4.038, p< .05). Only children (m=15.80, sd= 3.11) and first-born children (m=15.09. sd=3.11) were more intelligent than middle children (m=11.76, sd=2.71) and last-born children (m=11.76, sd=2.71).

The hypothesis that only children and first-born children would have a higher level of intelligence was supported by the data. The data are congruent with the Confluence Theory (Rodgers, 2000), and with Nyman`s (1995) findings. The data are also congruent with Alfred Adler`s theory of family constellation (Engler, 2000) which was the first of it`s kind. As with any study, there are limitations to this one. Although the participants varied in age, the were homogenous in many other ways. Obviously, if a person is in college, he or she is somewhat intelligence, so this could have also skewed the results. The tests weren`t done in an official manner, so if they would have been, maybe the scores would have been different. Because of the limitations of the study, it is questionable if the results could be generalized to the general population. College students were the participants and they aren`t a valid sample of the general population. Since this study can`t be applied to general population, future researchers should use a wider sample size, including adults of all educational levels. Another way this study could have been improved is to study children in the same family. If this were done, it could be found that intelligence does run in the family and isn`t a result of birth order. This would be sure to provide more insight to the ever growing debate on birth order and intelligence.

Ceci, S. (2001). Intelligence: The surprising truth. Psychology Today, 34, 46-52.Engler, B. (1999). Personality Theories: An introduction. Boston: Houghton Mifflin.Nyman, L. (1995). The identification of birth order personality attributes. Journal of Psychology Interdisciplinary & Applied, 129. 51-60.Pines, M. (1981). Only isnít lonely. Psychology Today, 13, 15-20.Rodgers, J. (2000). Are firstborns smarter? Psychology Today, 33, 20.Schachter, S. (1963). Birth order, eminence, and higher education. American Sociological Review, 2, 757-767.Terry, W.S. (1989). Birth order and prominence in the history of psychology. The Psychological Record, 6, 333-337. Zanjonc, R.B., Markus, G.B., Berbaum, M.L., Baugh,J.A., & Moreland, R.L., (1991). One justified criticism plus three flawed analyses equals two unwarrented conclusions: A reply to Retherford and Sewell. American Socialogical Review, 56, 159-165.

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Please give the following demographic information:

Sex: Male Female


Status at MWSC: Freshman Sophomore Junior Senior

Birth Position: Only Child First Born Middle Child Youngest Child

Submitted 11/29/2001 11:12:43 AM
Last Edited 11/29/2001 1:41:30 PM
Converted to New Site 03/09/2009

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