Birth Orderís Effect on Primary Friendship Selection as a Function of Family Size




Ashley Bahnken

Byram Hills High School

Armonk, NY











Section I

Human beings have the natural inclination to ponder the things that frame their day to day lives. After all, isnít it only natural to question the world around us? Some of the greatest inventions have arisen out of an individualís sheer curiosity to explore something that fascinated them. Others have arisen after an attempt to simplify a task or improve everyday life. We can trace this idea back to a man who went by the name of Benjamin Franklin. Unfortunately, poor Ben had inadequate eyesight and was forced to wear glasses when he wished to read. Naturally, he grew tired of continuously taking them on and off. He realized he must devise a way to use his glasses for both near and far. He resourcefully cut two pairs of spectacles in half and put one of each in a single frame. Today, we still use what Ben named bifocals. Benís curiosity and desire to better something that was close to him led to a device that continues to be used today all over the world.

The idea for my research arose in a similar manner. However, my inspiration was elicited directly from a curiosity pertaining to my own personal development, rather than a desire to simplify a task or to improve my day to day life. I was sitting in the waiting room of a doctorís office in Manhattan one day when I stumbled upon an article concerning "only" children. As an "only" child myself, I was intrigued by how the absence of siblings could shape my personality. As I read on, not only did I see that this was the topic for me, but also that there was an abundance of birth order literature that already existed. As I began reading articles about birth orderís effect on onlies, first, middle, and last borns, I began to see that birth rank has been shown to have very specific effects on oneís personality. For instance, I learned that an individualís birth order can have a profound effect on a personís drive to succeed, as well as his or her likelihood to be social. Since I am also interested in clique formation, I began exploring how a personís birth order may affect his or her social interactions. Soon enough, I began forming my own hypothesizes about birth orderís effect on social interactions.

I tested my idea by surveying one hundred seventy seven subjects. Their ages ranged from 18 to 25 years. Participants were students at Pace University, in Pleasantville, New York and Iona College in New Rochelle, New York. I designed a three part survey that was distributed to every participant. The first section requested demographic information, about the participantís age, gender, marital status and "major of study" (or reason for attending college). The second section asked each participant to describe his or her familyís structure. Participants listed the ages of their siblings from oldest to youngest and indicated whether each person was a brother, sister or self. The final part of the survey asked participants to describe the birth order of the three people that they consider their closest friends.

A school based IRB (Institutional Review Board) was also obtained prior to distribution. Consent forms were attached to every survey. As the surveys were distributed, a verbal statement of minimal risk was given. Participation was voluntary. Each participant was informed that they could decline participation at any time during the study without reason or prejudice. Participants were told not to write their names on their surveys so that their responses would be entirely anonymous. They were told that none of the information collected would be connected to their identity. There was no time limit for completing the survey, but most surveys were completed in less than 10 minutes. Once the survey was completed, consent forms were detached and kept by every participant.

Essentially, the intersection between science and math allowed me to create this experiment. The basis of my idea relates to science, but I was only able to test it through the use of statistical analysis. While my sample size was relatively small, we are able to extend what my results suggested to the overall population. This, in sum, is what makes the connection between math and science in the research process so crucial.

My day to day tactical work was directly supervised by my research teacher while my strategic thoughts were supervised more closely by my mentor, Dr. Toni Falbo, who is a professor at the University of Texas at Austin. Together, we designed by survey, discussed analysis and developed ideas for the future.

Through my research, I have learned how valuable every studentís contribution to the overall body of scientific knowledge truly is. While all of our ideas are sparked by something unique, it is often the simple things that grab our attention and cause us to ask questions and begin to brainstorm. My idea was sparked by the desire to better understand myself, yet resulted in a finding that was novel and unique to any one elseís. Certainly, we donít all have to find the cure for cancer in order to make a valuable contribution to science. Everybodyís thoughts truly are important.

Section II

As I mentioned previously, my research focused on birth order, or the numerical position of in individual in the order of births in his or her family. Over 1000 studies have either focused on, or incorporated birth order into their research design (Ernst and Angst, 1983). Numerous renowned researchers now recognize birth orderís important effect on a childís behavior, personality and performance (Grose, 2005). Yet, there has been a dearth of literature studying birth order and the formation of platonic relationships. My study quantified birth orderís effect on platonic social network formation.

Birth Orderís Foundation

Alfred Adler was an early identifier of birth order as a significant factor in personality development (Hjelle and Ziegler, 1992). He reasoned that, "even though children have the same parents and grow up in nearly the same family setting, they do not have identical social environments" (Hjelle and Ziegler, 1992). Other research continues to support many of Adlerís ideas. For example, Ernst and Angst (1983) note that differing birth positions of children elicit different methods of socialization from parents toward their children. Similarly, Moore, Cohn, and Campbell (1997) showed that parents interact differently with each of their children. Additionally, Richardson and Richardson (1990) stated that inter-familial experiences may be almost as diverse as separate familial experiences.

Why Offspring Are Treated Differently by Parents

Various rationales for the apparent inconsistency of treatment toward children as a function of birth order have been suggested in the literature (Claxton, 1994). One states that parents treat their children differently as a result of differing expectations that they hold for each child, depending on their age (Kalmuss and Davidson, 1992). Adults seem to place higher expectations on first borns and tend to regard their first borns more positively than subsequent arrivals (Kalmuss et al.,). Only children experience this too, as they are in some ways "permanent first borns". Research has suggested that parents impose exceptionally high standards on only children (Clausen, 1966; Kammeyer, 1967). Parents may also unconsciously treat each of their children differently as they attempt to disperse their time and resources "evenly" (Sulloway, 1996; Salmon and Daly, 1998; Hertwig, Davis and Sulloway, 2002). As there is a limit to the resources that they have to offer, it can be very difficult for parents to treat each child identically. Thus, parents treat each of their children differently in response to birth order differences.

As a result, each child responds to their specific parental treatment and develops personality characteristics accordingly. It follows then that each rank develops similar characteristics that are common to other children of similar rank. For example, a first born in Family A will exhibit similar characteristics to a first born in Family B.

Since this research categorizes individuals based upon their birth order rank, and because correlations will be investigated based upon this categorization, it is important to review the recognized base characteristics of each birth order rank.

Table 1: Summary of Birth Rank Fundamental Characteristics

Birth order

Base characteristics

First borns

  • Conscientious (Leman, 2000)
  • Ambitious (Richardson & Richardson, 1990)
  • Well organized (Leman, 2000)
  • Goal-oriented (Hjelle & Ziegler, 1992)
  • Believers in authority (Hjelle & Ziegler, 1992)
  • Perfectionists (Leman, 2000)
  • Self-reliant (Richardson & Richardson, 1990)
  • Highly motivated (Leman, 2000)
  • Self critical (Leman, 2000)

Only children

  • Frequently exhibit traits of first borns (Brophy 1989, p. 54).
  • Highly motivated (Claxton 1995, p.27)
  • Confident (Claxton 1995, p.27)
  • Achievement oriented (Claxton 1995, p.27)
  • Outgoing (Brophy 1989, p. 55)
  • Less competitive than other birth orders (Claxton 1995, p. 27)

Middle children

  • Competitive (Bohmer and Sitton, 1993)
  • Often formulate a unique identity that sets them apart from their siblings (Buckley, 1998)
  • Less close to parents, and more so to friends and siblings (Salmon and Daly, 1998)
  • Mediators (Leman, 2000)
  • Choosey about who they confide in (Leman, 2000).

Youngest children

  • Charming (Leman, 2000)
  • Attention seeking (Nims, 1998)
  • Social (Leman, 2000)
  • Tenacious (Leman, 2000)
  • Jealous (Buunk, 1997)
  • Affectionate (Leman, 2000)
  • Spontaneous (Leman, 2000)

Birth Orderís Connection to Social Interaction: The process of building upon previously established knowledge

Historical research by Gillies (1976) stated that when a relationship is romantic, then the relationship tends to focus on personality differences; however, when that relationship is strictly of a platonic friendship nature, then the individuals in that relationship tend to focus on similarities. Similarly, Katz (1979) believed that those with similar personalities, morals, and level of maturity get along better than those who generally are not aligned on such issues. This suggests that, since people of each birth position exhibit characteristics that are common to otherís of that position, and since people are most compatible in platonic relationships when they exhibit similarities, birth order should have an effect on the formation of platonic social networks.

Despite the preceding evidence suggestive of birth orderís effect on social interaction, there is a paucity of literature relating birth order as a determining factor in friendship formation. Furthermore, Sulloway (1996) has suggested that birth order researchers have consistently failed to control potentially confounding variables such as family size. Leman (2000) has stated that a personís physiological birth order changes depending on the size of the family. To illustrate, in a family of two, the second born child is considered the last born. However, in a larger family, the second born child is not considered a youngest child despite the fact that he may have developed many similar characteristics to the second born in the small family prior to the birth of the subsequent siblings. This research focuses on birth orderís effect on the formation of platonic social networks as a function of family size.


My chi square analysis revealed that first borns and only children are significantly affected by their birth rank as they form platonic friendship bonds with others. The only child seems to be especially influenced. All of the experiences that first borns undergo before another child is born (undivided parental attention, unlimited resources, etc), are experienced by an only child for his or her entire life.

Middle children and youngest borns seem to be less affected by their birth rank as they form platonic friendship bonds. Perhaps this is because many variables are introduced after the first born child. These variables include number of children born after the first born child (family size) and number of years between each sibling. Leman (2000) has stated that a personís physiological birth order changes depending on the size of the family and the number of years between each child (Leman, 2000).

Finally, while it is expected that one in three of a person's friends listed will have same birth order as that person, this is only true if each rank is of equal frequency in the general population. However, a difference is likely to exist. In 2000, the Census Bureau reported that the average number of children per family was 1.86. This means that there are many single child families and families with only two children. Thus, middle children are now less prevalent in the general population since a minimum of three children are needed for a middle child to be considered a middle child. This may be why middle children displayed a weaker correlation between their birth ranking and that of their friends compared to only children, first borns, and last borns.

To address this problem, we can look at birth cohorts, which are defined by the US Census Bureau as groups of people who were born in a specified calendar period. Every participantís birth cohort must be determined. This can be done by looking at participantís age or birthdate. If there is little variation in respondentsí ages, then you can assume they are in the same cohort. If they vary in age, they vary in birth cohort and you would have to look into the census about the number of children women had during that cohort. Then, the number of children women had during that cohort can be obtained from the U.S. Census Bureau. This information can be used to determine the total number of only children, first borns, middle borns and youngest children.

Research Significance

This research was significant in that it was the first study to find a correlation between an individualís birth order and that of their friends. While research has been performed concerning birth order and romantic partnership, no studies have yet found a relationship between birth order and platonic friendship bonds. This study found that only children and first borns from small and large families are significantly affected by their birth ranking as they form platonic friendships. It is important to note that, while many birth order studies fail to control the confounding variable of family size (Sulloway, 1996), this study separated first borns from small families from first borns from large families. This was done in the same way for last borns.

While no person can change his birth order, an understanding of its effect on personality can be extremely beneficial. For instance, that the seemingly positive achievement oriented characteristics that help oldest children succeed academically and professionally are the same characteristics that can potentially damage close relationships they have with others. First borns and only children must keep in mind that the high expectations that they place upon themselves cannot be expected of every person they interact with. Middle children must remember that the feeling of personal triumph comes from within and needs not to originate from surpassing another personís achievement. Youngest children must recognize that they will not be "babied" forever and must remember to maintain some form of self-direction. My research suggests that understanding birth order differences may also help in individual therapy as well as family therapy, particularly to problems concerning sibling rivalry.