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Does Birth Order Impact Intelligence?

Does Birth Order Impact Intelligence?

Missouri Western State University


Birth order and its impact on the individual have been a matter of great debate among researchers for over a century. Many say that the first-born children are the smartest out of all the other siblings in a family. We conducted our own study by distributing a short IQ test consisting of questions about birth order, to 100 participants. We discovered that birth order does have a slight impact on IQ. Overall, first-born children and only children scored higher on the IQ test than did later born children. Therefore, this study suggests that first-born and only children perform better on IQ tests and overall are more intelligent.


If you were to ask yourself to come up with a list of things that everyone is born with; you could probably come up with lots of things. Unfortunately, birth order would probably not be one of them. There is no escaping this; everyone has an order of birth or ordinal position within the family such as the first, second, third or youngest, middle, or oldest child. Parents often times use these categories when introducing their children to someone such as “I would like you to meet my youngest son.” There have been tremendous amounts of research on this topic because it is easy to talk about and it is something that everyone can relate to.
Scholars have studied the effects of birth order as far back as the time of Galton, who in 1864 observed a uneven number of eminent British scientists and believed in the superiority of the eldest (Pfouts, 1980). In 1918 Alfred Adler discussed his views of birth order and the family constellation. He thought that before one could be judged, we should know what environment the person grew up in. Each birth order position puts different demands on the child, which influences his views and adopts a style and attitudes that correspond with that perceived position (Manaster, 1977).

One area that has generated much research is whether or not birth order has an impact on a person’s intelligence. “Is the oldest the most intelligent?” and “Does the order in which you are born, effect your intellectual development?” are just a few common questions that researchers try to answer. Rodgers, Cleveland, Van den Oord, and Rowe (2000) believe that the link between birth order and intelligence is all a “methodological illusion” because of the different results one can get from using different methods. They point out that very often parents look for causal explanations for their children’s behavior and escape responsibility or accountability. For example “Sue is moody because she is an only child” or “Tommy is not more of an achiever because he has so many siblings to compete with.” In conducting their own studies that used within-family data they found no consistent relationship between birth order and intelligence.

Zajonc (2001) is one of the leading researchers who believe that birth order does impact a person’s intelligence. He has developed what has been termed the confluence model with the idea being that the intellectual growth of every member is dependent on the others in the family. The model shows that each successive sibling is born into a weaker intellectual environment and that intellectual performance increases with decreasing family size. When the gaps are short children who are born early in sibship perform better on intelligence tests that do later children (Zajonc, Markus & Markus, 1979).

The reasoning behind this is that firstborns are able to gain an intellectual advantage through the teaching effect or becoming tutors and mentors to the younger siblings. Many times parents call on the older siblings to help the younger siblings by answering questions, giving explanations and offering meanings of words all of which helps explain why firstborns gain more verbal fluency quicker (Zajonc, 2001). Last-born and only children do not have they opportunity to become tutors and therefore suffer from a “last-born handicap” (Retherford and Sewell, 1991).

The debate on the two sides of the issue of whether or not birth order impacts intelligence is far from being over. The purpose of this study is to help generate new ideas and to add to the body of research. The main focus was to determine whether or not birth order impacts a person’s intelligence.

One hundred questionnaires were distributed to students at Missouri Western State College, who are enrolled in Psychology classes. To get a representative sample, we collected data from a variety of backgrounds. That is why we used various levels of psychology classes, and a combination of male and female students.

The survey is composed of a pen and paper questionnaire with two parts. The first part included a section with 14 IQ test questions. These questions were randomly selected from H. J. Eysenck’s book “Know Your Own IQ” and from www.Queendom.com. The second part included questions involving themselves and family members, to assess birth order and IQ.

Questionnaires were handed out at Missouri Western State College to various individuals enrolled in Psychology classes. The participants were instructed to complete the two parts of the questionnaire that was self-explanatory. The participants were asked not to put their name on the questionnaire and were given approximately ten minutes to complete it.

A Pearson correlation coefficient was used to calculate whether or not there was a relationship between participant’s birth order and their IQ. Our findings showed a weak correlation of .195(p=.05) between the participants IQ and birth order.
The gender of the participants was also taken into account, to find out whether or not males had higher IQ scores than females. The independent sample t test showed no significant difference in IQ’s of males and females (t(98) = .62, p = .537

The purpose of this study was to determine whether or not a person’s intelligence is impacted by their birth order. In the sample of 100 college students who participated in this study, the findings showed that there is an impact with a weak correlation of .05. These findings were consistent with our hypothesis and majority of the literature found by Zajonc (2001) and several other researchers. Earlier born children tend to be smarter than later born children within the family.
In this study we did not take into consideration individuals who were adopted, foster, and step children. Other limitations with this study are that the ages of the participants varied and all were in college, which could have made a difference in the IQ scores and results because college students are already tend to be more intelligent. The actual IQ test we used was not official and probably lacked the capability of testing in all the areas needed to evaluate a person’s IQ. If this study would be repeated the IQ test could be more standardized with a larger number of questions on it. The sample of participants should be from all different educational levels and not just a sample of those in college.

For additional information male and female scores were compared in this study to see if one gender scored better on the IQ test. We found there to be no significant difference between the two groups. Birth order is just a small fragment of many other things that impacts an individual’s intelligence. We believe that for future research other things such as parenting style, gender, race, and socioeconomic status should also be taken into account when looking at what impacts a person’s intelligence.

This is an important area of research, perhaps an area that can be expanded on significatly more. The knowledge of a person’s birth order could be useful in school settings to help explain why some students do better than others. Therapy is also another area that knowing a person’s birth order could be helpful in family sessions, particulary pertaining to sibling rivalry problems.

Manaster, G. J. (1977). Birth order: an overview. Journal of Individual Psychology, 33, 3-8.
Pfouts, J. H. (1980). Birth order, age spacing, IQ differences, and family relations. Journal of marriage and the Family, 42, 517-531.

Retherford, R. D., & Sewell, W. H. (1991). Birth order and intelligence: further tests of the confluence model. American Sociological Review, 56, 141-158.

Rodgers, J. L., Cleveland, H. H., Van den Oord, E., & Rowe, D. C. (2000). Resolving the debate over birth order, family size, and intelligence. American Psychologists, 55, 599-612.

Sternberg, R. J. (1997). The concept of intelligence and its role in lifelong learning and success. American Psychologists, 55, 599-612.

Zajonc, R. B. (2001). The family dynamics of intellectual development. American Psychologist, 56, 490-496.

Zajonc, R. B., Markus, G. B., & Markus, Hazel (1979). The birth order puzzle. The Journal of Personality and Social Psychology, 37 (8), 1325-1341.

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