The Effects of Birth Order on Interpersonal Relationships

Renee M. Schilling



The researcher attempted to determine whether an individual’s place in the family, known as “birth order”, affected that person’s types of relationships. Three types of relationships were studied: same-sex friendships, opposite-sex friendships, and opposite-sex romantic relationships. Participants report the birth order of themselves as well as the birth order of the people with whom the have/have had interpersonal relationships (N = 91, with 21 males and 70 females). Analysis of the data indicated no significance between birth order and the three types of successful romantic relationships. However, birth order did have an affect on unsuccessful romantic relationships in this study. This research is important because all of the existing research regarding birth order is inconclusive, as exemplified in the literature search. Furthermore, no research has been found examining the effects of birth order on friendships and unsuccessful romantic relationships.


The Effects of Birth Order on Interpersonal Relationships

            Many studies have been done in an attempt to determine what exactly makes people who they are. Personality has many different definitions. Furthermore, many factors shape the formations of one’s personality. These statements are fairly obvious. One factor in particular has been researched more closely than all other factors related to development. This factor is birth order. Birth order refers to the numerical place of a person in the order of births in his or her family (Ernst & Angst 1983).

            Birth order has been relevant in many research studies. Each rank, the oldest, middle, youngest, and only, generally have similar characteristics that are common in different people of the same birth order. It is logical to conclude that these similar characteristics will effect other aspects of life, namely interpersonal relationships. If the birth order factor has a major influence on an individual’s personality, and different people of the same birth order have similar personality traits, then this researcher concludes that birth order has a major influence on the types of interpersonal relationships people have.

            Although much research has been done involving birth order, the research is inconclusive. Nyman (1995) found that most research has been involved in determining traits of oldest children. Nyman’s study had individuals list three characteristics, negative or positive, for each of the birth orders. He found that the participant’s own birth order did not affect their answers. Instead, the participants recorded stereotypical general traits that each birth order has as a reputation. This suggests that regardless of birth order, people generally view the birth orders the same. In this case, oldest was favored most, followed by middle, youngest and only. Therefore, perhaps the perceptions a person has about a particular birth order will influence their decisions about interpersonal relationships.

            It was Alfred Adler who first recognized birth order as a significant factor in personality development. Adler believed 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 & Ziegler 1992). Adler also reported the characteristics that the various birth orders seem to share. The oldest child tends to be conservative, power-oriented, and predisposed towards leadership (Hjelle & Ziegler 1992). The only child, according to Adler, tends to be dependent and self-centered (Hjelle and Ziegler 1992). Adler is also quoted as saying, “The only child has difficulties with every independent activity and sooner or later they become useless in life” (Leman 2000).  Furthermore, the middle child is usually achievement-oriented, but may set unrealistic goals that will end in failure. Finally, the youngest tends to be highly motivated to outdo older siblings in various accomplishments (Hjelle & Ziegler 1992).

            Walter Toman (1961) is also a big name when it comes to birth order. His book, Family Constellation, discusses not four birth order positions, but eleven. These include:  oldest brother of brother(s), youngest brother of brother(s), oldest brother of sister(s), youngest brother of sister(s), the oldest sister of sister(s), the youngest sister of sister(s), the oldest sister of brother(s), the youngest sister of brother(s), intermediary sibling position, the only child, and twins (Toman 1961). This makes birth order more complicated when measuring characteristics and types of relationships. However, further research supports the fact that family size and sex siblings do impact the birth order factor (Toman 1961).

            Since both Adler’s and Toman’s research was conducted between forty and sixty years ago, another source was consulted for the general characteristics of the various birth orders. Kevin Leman’s (2000) book, The New Birth Order Book: Why You Are the Way You Are, discusses many factors involved in measuring birth order, as well as the stereotypical traits that each birth order tends to possess. Leman (2000) suggests that there are nine important factors to consider when examining birth order:

Spacing - the number of years between children

The sex of each child - and in what sequence males and females are born

Physical, mental, or emotional differences – yes, genes are important

Sibling deaths – which, if occurring early, cause the child below to be “bumped up” to the next birth order

Adoptions – which may or may not have an effect on birth order, depending on how old the child is when adopted

The birth order position of each parent – first-born parents usually run a much different ship than later borns

The relationship between parents – and the parenting style they use as they pass on their personal values to their children

The “critical eye” of a parent – constant criticism takes its toll

The blending of two or more families – due to death or divorce – in a stepfamily certain birth orders often get stepped on (Leman 2000, pp33-34).

Leman’s research on birth order personality characteristics supports Adler’s findings in most respects. Leman (2000) reports that oldest borns tend to be conscientious, well organized, serious, goal-oriented achieving, believers in authority, reliable, perfectionists and self-reliant. He also states that these seemingly positive, motivated characteristics that help the oldest child to succeed academically and professionally are the same characteristics that damage close relationships they have with others. Leman (2000) disagrees in some respect with Adler when it comes to the characteristics and reputation of only children. Leman (2000) says that only children tend to be confident, perfectionist, organized, ambitious, logical and scholarly. Though only children can be self-centered, it is not to the extreme that the existing stereotypes indicate. Furthermore, only children take some of these traits, namely perfectionism, into their interpersonal relationships. This results in high expectations for anyone an only child comes in contact with (Leman 2000). Middle children have a list of contradictory personality characteristics: loner/sociable, impatient/laid-back, aggressive/conflict-avoider. This suggests that middle children do not have a certain list of general characteristics like the other birth orders. Leman (2000) did say that middle children tend to be mediators and are choosy about who they confide in. Middle children also are one of the most monogamous birth orders, who are motivated to make their marriages and families work. Middle children also tend to have the less problems than first-born/only children. All of these qualities deal with their relationships with people (Leman 2000). Youngest children tend to be charming, people-oriented, tenacious, affectionate and attention-seeking. They also tend to just “do” things – without thinking about the consequences of their actions. This is a trait that would come into play during relationships as well (Leman 2000).

            Ernst and Angst (1983) developed research that examined the importance of the sex of the siblings. This study proposed the imitation hypothesis and the contrast hypothesis (Ernst & Angst 1983). In the imitation hypothesis, the researchers expected the child with an opposite sex sibling to develop characteristics of that opposite sex (e.g., a girl with a brother will be less feminine than a girl with a sister). The contrast hypothesis argued that the opposite-sex sibling would strongly reinforce stereotypical gender roles (e.g., a girl with a brother will be more feminine than a girl with a sister). This is an important factor in determining the formation of close friendships (Ernst & Angst 1983).

            Further studies have been done that examine the effects of birth order on other factors. Most of the research did not relate directly to interpersonal relationships. However they all related to a specific factor in a relationship. A study done by Buunk (1997) examined relationships between jealousy, personality and attachment styles. This study found that laterborns were more jealous than firstborns.  Furthermore,  since all other variables were controlled, birth order was the only factor left with which to associate feelings of jealousy (Buunk 1997). Another study, completed by Bryce and Schwebel (1996), examined birth order, gender and irrational relationship beliefs. Surprisingly, Bryce and Schwebel found that oldest children have the highest number of irrational beliefs, while youngest have the least amount. Gender, in this case, had no effect.

            Birth order, sex of siblings and self-ratings of interpersonal power were examined in a study done by Todd, Friedman and Steele (1993). Their findings were that older sisters of younger brothers rated themselves as very high in power. Younger sisters of older brothers rated themselves as very low in power (Todd, Friedman and Steele 1993). This research suggests that any given birth order’s perception of interpersonal power will be carried over into that individual’s interpersonal relationships. An additional study done by Phillips, Long and Bedeian (1991) looked at Type A status and birth order. They found that oldest and only children score higher on Type A status than the other birth orders. This, too, could affect relationships with people among various birth orders. One final study, which also supports the effects of birth order, was done by Harris and Morrow (1992). They examined birth order and gender as it relates to responsibility and dominance. Oldest males and youngest females had higher dominance scores than the rest of the birth orders. The factor of dominance could affect interpersonal relationships as well (Harris & Morrow 1992).

            There are studies involving birth order which indicate no significant results. One such study was done by Angira (1990) on birth order, family structure and adjustment. The results indicated that there was no significant interaction between family structure and birth order. However, this study did say the birth order and family structure significantly impacted adjustment. The way in which birth order impacted these factors was not specified.

            Same-sex and platonic friendships have not been researched as often, specifically with birth order as a determining factor. One theory was researched regarding friendship versus romantic relationships (Gillies 1976). Gillies stated that when a relationship is not platonic, then the relationship focuses on differences; however, when that relationship is strictly of a friendship nature, where sexuality is outside of it, then the people in that relationship are focusing on similarities.

            Conversely, a variety of studies have been done to determine the effect of birth order on marriage partners. Leman’s (2000) research suggests the ideal and not so ideal birth order pairs for long-term romantic relationships. Leman (2000) has found that the absolute worst birth order pairs are those within the same birth order (e.g., two first-borns/onlies, two middles, or two youngest). He says that two first-borns together equals a lifelong power struggle. Leman (2000) also says that two middles are a bad match because communication will be lacking due to avoidance of conflict, a natural trait of middle children (as discussed earlier). Leman (2000) also says two babies are not a great match because youngest children usually do not delegate responsibilities well, and assume that someone else will pick up the slack. If there are two people that are both assuming the other will pick up the duties at home, then the household will more than likely fall apart. According to Leman (2000), it is best to marry outside your birth order. On top of that, it is best to marry the most opposite birth order position.

            Research by Toman (1964) supports Leman (2000). Toman (1964) examined the choice of marriage partners by men who only had brothers. Toman (1964) found that choices of wives for oldest brothers tend to be that of youngest sisters. Furthermore, the choices of a wife for youngest brothers tended to be oldest sisters (Toman 1964). Conversely, Levinger and Sonnheim (1965) conducted a study that negates Toman’s study. Their data failed to confirm Toman’s view that marital adjustment increases with dissimilarity in the partners’ birth orders. In additon, Agnthotry (1986) completed research on a similar topic, the difference being that Agnthotry’s research was not limited to one gender. Agnthrotry (1986) found that the best marital adjustment occurs when both spouses are older than their opposite sex siblings. The worst match occurs when both spouses are younger than their opposite sex siblings. Another study, looking at birth order and degree of marital satisfaction, found that the oldest brother and youngest sister reported the most marital satisfaction (Plhakova & Osecka 1993).

            The most interesting study found during this literature review was conducted by Peter Murdoch (1966). The study dealt with birth order and age at marriage. Murdoch said that first borns are more dependent than later borns (which is contrary to the research that states they are the independent birth order) and also learn that anxiety is reduced when one is with other people. Based on these two assumptions, Murdoch (1966) hypothesized that first borns tend to marry earlier than later borns. He found that oldest males do, on average, marry earlier than later born males. First born females did not actually marry earlier, but they did talk about getting married earlier than later born females. Furthermore, when asked to say when the best age is to get married, the mean for oldest females was lower than that of later born females (Murdoch 1966).

            This research is meant to add research to the existing literature on birth order’s effect on romantic partners (both successful and unsuccessful). However, the research is unique in that it is examining the effect of birth order on friendship as well, which is a less studied area. In order to study the effect of birth order on interpersonal relationships, a fifteen-item survey was distributed, asking the participants about their birth order and about the birth orders of people they have or have had interpersonal relationships with (see appendices A & B). This researcher’s conceptual hypothesis says that the types of relationships people form are effected by birth order. Five operational hypotheses are examined in this study: First, if an individual reports having a close friendship with someone of the same sex, then that person will report that he/she and the friend have the same/similar birth order; Second, if an individual reports having a close platonic friendship with someone of the opposite sex, then that friend will be reported as having the same/similar birth order as the participant; Third, if an individual reports having a successful romantic relationship with someone, then that romantic partner will be reported as having an opposing, but compatible birth order than that of the participant; Fourth, if an individual reports having been divorced, then that person will report that he/she and the divorced person will have the same/similar birth order positions; And, fifth, not counting the divorce, if a person reports having had an unsuccessful romantic significant romantic relationship (that has lasted at least two years), then that person will report that he/she and the ex-romantic partner have similar birth order positions. All of these hypotheses are consistent with Leman’s (2000) research on ideal marriage partners for the various birth orders and Gillies’ (1974) research on friendships.



            20 males and 71 female participated in the research, ranging from 16 to over 60 years in age. Participants were chosen at three different places of employment: one which was predominantly male (car dealership), one which was predominantly female (nursing home), and one which was presumably equally mixed between the two sexes (insurance company). Participants were given a survey in the work environment and gave verbal consent to completing the anonymous surveys. The researcher was also present at all the locations to answer any questions about the survey. 40.7% of the sample reported being firstborns; 31.9% of the sample reported being middle children; 23.1% of the sample reported being the youngest in their families; and 4.4% of the sample reported being only children.


            A fifteen-question survey (see Appendix A & B) developed by the researcher was distributed. Demographic data included gender, age and a list of the participant’s sibling(s)’s gender and age. The remaining questions asked yes/no questions about whether or not the individual had a same-sex friend, an opposite-sex friend, and a current romantic partner. Participants were also asked if they had ever been divorced or had had a significant unsuccessful romantic relationship (not counting a divorce and one which has lasted two or more years). If the participant answered “yes” to any of these questions, a follow-up question about the birth order of the person in which the participant has/had the relationship with was included.


            As mentioned before, the survey was distributed in three different work settings in an attempt to balance the overall gender percentages in the study. The nursing home was composed of all females, the car dealership of all males and the insurance company was presumably mixed. The researcher controlled for day of the week and time of the day – all of which was Friday mornings. The surveys were given out on three different Fridays at the same time so the researcher could be present for any questions. There was no time limit for completing the surveys, but the total time spent at each place of employment did not last longer than an hour.


            The reliability for the survey was .694. Frequencies were computed for all of the variables measured in the survey. Out of the 91 participants surveyed, 37 were oldest children, 29 were middle children, 21 were youngest children and 4 were only children. 19 participants reported being divorced, and 40 participants reported having had an unsuccessful significant romantic relationship outside of a divorce. 82 of the 91 participants reported having a close same-sex friend, 49 reported having a close opposite-sex friend and 75 reported having a current romantic relationship.

            Chi-squares were computed for each of the five original hypotheses the researcher set out to investigate. The first hypothesis, regarding the birth order of the participant and the birth order of a close same-sex friend, was not significant (chi=5.09, p=.826). The second hypothesis, regarding the birth order of the participant and the birth order of a close opposite-sex friend, was also not significant (chi=9.225, p=.417). The third hypothesis, regarding the birth order of the participant and the birth order of the individual’s romantic partner, was not significant (chi=10.092, p=.343). The fourth hypothesis, regarding the birth order of the participant and the birth order of the most recently divorced partner, also was not significant (chi=7.996, p=.535).

            The fifth and final hypothesis was also tested using a chi-square. This hypothesis stated that if an individual reports having had an unsuccessful significant romantic relationship (not counting a divorce and that has lasted for two or more years), then that person will report that he/she and the ex-romantic partner have the same/similar birth order positions. Out of the 91 participants, 40 reported having had an unsuccessful significant romantic relationship. This final hypothesis turned out to be significant (chi=16.711, p=.05). In order to determine in which way birth order of the participant and the birth order of the ex-romantic partner were related, the cross-tabulation was examined (see Table 1 below).

Unsuccessful Romantic Partner’s Birth Order

Birth Order of the Participant





























































Table 1 indicates that both the birth order of the ex-romantic partner and the birth order of the participant were usually the same/similar birth order


The results of the cross-tabulation indicates that the original hypothesis was supported in this research. For three of the four named birth orders (oldest, middle and only), the highest amount of unsuccessful partnerships occurred when that ex-partner was of the same/similar birth order of the participant (same/similar applies to oldest and only – these are considered very similar birth orders).

            Other analyses were done to examine additional relationships between the measured variables. Among these were looking at just the oldest and youngest children’s interpersonal relationships. Since a lot of the research indicated that the ideal romantic partnership was that of an oldest and a youngest, it was logical to assume that some of the results would be significant. However, this did not happen. Another test was done to see if there was a difference between age groups in the sample. Results indicated no significance.


            There were five original hypotheses. The first one stated that the birth order of the participant and the birth order of the same-sex friend would be the same/similar. This turned out to be not significant. 81 of the 92 participants reported having a close same-sex friend. This and the fact that the p-value was high at the .826 level suggest that birth order does not impact same-sex friendships.

The second hypothesis stated that the birth order of the participant and the birth order of the opposite-sex friend would also be the same/similar. Again, this turned out to be not significant at a p=.343 level. However, there was also a problem with the placement of the questions on the survey regarding opposite-sex friend and romantic partner. It was visible to the researcher that at least on seven occasions the opposite-sex friend and the romantic partner reported were one in the same due to the unique birth orders reported(e.g., on one occasion, the opposite-sex friend’s birth order was fifth of ten, as was the romantic partner’s – this seemed a little off to be just a coincidence). Furthermore, only 49 of the 91 participants reported having an opposite-sex friend. Both of these factors indicate that there needs to be a bigger sample and the survey would have to be adjusted so that the questions are clear in what they are asking. In addition, there was a question regarding how long the participant and the current romantic partner had been together. The answers ranged from one month to over twenty years. This factor alone could have skewed the results slightly. All in all, this research did not support the researcher’s initial hypothesis.

            The fourth hypothesis stated that the birth order of the participant and the birth order of the divorced person would be the same/similar. This also turned out not to be significant on a p=.535 level. However, of the 91 participants, only 19 reported being divorced. Because of this, the researcher believes a bigger sample is needed. The original hypothesis regarding divorce and birth order was not supported by this research.

            The fifth and final hypothesis is more interesting. It stated that the birth order of the participant and the birth order of the ex-romantic partner would be the same/similar. This turned out to be significant at the p=.05 level; also, the results were in the same direction as the original hypothesis. So, the fifth hypothesis was supported by this research. This final result suggests that perhaps birth order does not have a significant impact on the successful relationships. Instead, this research indicates that birth order has a significant impact on with whom we do not have successful relationships with. The research also suggests that this impact is so significant that these relationships, though lasting a relatively long time, ended before marriage could occur.

            Of course, there were many problems with this particular study. Some have already been mentioned – namely the problems with certain questions and the format of the survey. There were also many problems with the sample. One was that of the gender balance. Though the three places of distribution (car dealership, nursing home and insurance company) were chosen in an effort to balance the gender distribution of the sample, it backfired. This resulted in 77% females and 23% males. This sample is overly unbalanced. A 50/50 distribution would be preferred for future studies. Also, the three places of distribution were chosen because the ages of the people had good ranges, which should result in a variety of life experiences. However, this was not the case. In future research, people with more diverse happenings should be surveyed (e.g., more divorced people). Another problem was that of the birth orders of the participants. Surprisingly, the birth orders were well spread out with the exception of one. Out of 91 participants, only 4 were only children.

            One difficult factor to examine was that of the participant’s birth order. Leman (2000) stated many considerations on which birth order is measured. However, it was impossible to factor in all of those considerations. Even factoring in the sex of the siblings and the spacing of the births was difficult. In addition, this process was subject to the researcher’s opinion, which could have skewed the results. The birth orders reported by the participants about the people with whom they have/had relationships with was totally based on the amount of knowledge he/she had about that person. This is another factor that could have thrown the results slightly.

            For future studies, it would be interesting to divide the participants up into the three different work settings to see if there were differences between the groups. Also, instead of testing the biological birth order, perhaps it would be useful to determine the mental birth order by giving lists of traits of each birth order and having the participants choose which list best describes them overall. This could then be correlated with the biological birth order to see if it supports current research, and then be compared with the various interpersonal relationship types in this study.

            Because birth order has been argued as a factor in personality development, many research studies have been done examining birth order. However, because much of this research is either inconclusive or contradictory, more is needed to support or negate current research and theories.


            Agnthotry, Rekha. (1986). Marital Adjustment in Relation to Combinations of Ordinal Birth Position. Journal of Psychological Researches, 30(3), 150-155.

            Angira, K. K. (1990). A Study of Adjustment in Relation to Family Structure and Birth Order. Indian Journal of Current Psychological Research, 5(2), 69-72.

            Buunk, Bram P. (1997). Personality, Birth Order and Attachment Styles as Related to Various Types of Jealousy. Personality & Individual Differences, 23(6), 997-1006.

            Ernst, Cecile & Angst, Jules (1983). Birth Order: Its Influence on Personality. New York: Springer-Verlag.

            Gillies, Jerry. (1976). Friends: The Power and Potential of the Company You Keep. New York: Coward, McCann & Geoghegan, Inc.

            Harris, Kimberly A. & Morrow, K. Brent. (1992). Differential Effects of Birth Order and Gender on Perceptions of Responsibility and Dominance. Individual Psychology: Journal of Adlerian Theory, Research & Practice, 48(1), 109-118.

            Hjelle, Larry A. & Ziegler, Daniel J. (1992). Personality Theories: Basic Assumptions, Research, and Applications. New York: McGraw-Hill, Inc.

            Leman, Kevin. (2000). The New Birth Order Book: Why You Are the Way You Are. Minnesota: Baker Book House Company.

            Levinger, George & Sonnheim, Maurice. (1965). Complementarity in Marital Adjustment: Reconsidering Toman’s Family Constellation Hypothesis. Journal of Individual Psychology, 21(2), 137-145.

            Murdoch, Peter H. (1966). Birth Order and Age at Marriage. British Journal of Social & Clinical Psychology, 5(1), 24-29.

            Nyman, Lawrence. (1995). The Identification of Birth Order Personality Attributes. Journal of Psychology Interdisciplinary & Applied, 129(1), 51-60.

            Phillips, Antoinette S., Long, Rebecca G., & Bedeian, Arthur G. (1990). Type A Status: Birth Order and Gender. Individual Psychology: Journal of Adlerian Theory, Research & Practice, 46(3), 365-373.

            Plhakova, A. & Osecka, L. (1993). Sibling Constellations and Marital Satisfaction. Ceskoslovenska Psychiatrie, 89 (6), 376-383.

            Sullivan, Bryce F., Schwebel, Andrew I. (1996). Birth Order Position, Gender, and Irrational Relationship Beliefs. Individual Psychology: Journal of Adlerian Theory, Research & Practice, 52(1), 54-64.

            Todd, Judith, Friedman, Ariella, & Steele, Sharon. (1993). Birth Order and Sex of Siblings Effects on Self-Ratings on Interpersonal Power: Gender and Ethnic Differences. Individual Psychology: Journal of Adlerian Theory, Research & Practice, 49(1), 86-93.

            Toman, Walter. (1961). Family Constellation. New York: Springer Publishing Company.

            Toman, Walter. (1964). Choices of Marriage Partners by Men Coming from Monosexual Sibling Configurations. British Journal of Medical Psychology, 37(1), 43-46.