Birth-Order Effects on Facets of Extraversion – A Critical Review

‘Birth-Order Effects on Facets of Extraversion’ by Beck et al is an interesting study that makes the claim that our birth order (whether we are the eldest or youngest sibling) can effect our personality – specifically that first-borns are more dominant while their younger siblings are more sociable. If this study is correct then it sheds interesting light on our own personalities as well as others and can help us as parents and as social beings. This article then will examine the study in detail to determine whether the results can be taken seriously.

The aim of this study is to investigate whether birth-order has an affect on siblings’ personalities, in particular dominance and extroversion. The rationale for this is due to current inconsistent findings, and the reasons for inconsistencies. The abstract gives an effective overview of the study, stating the issue under investigation, the method used and the findings of the study. Together with the introduction, the concept and the aims of the study are made clear.

The introduction makes it clear what the study aims to find out, although there is no statement of practical implications the findings of the study will have. The first paragraph of the introduction just states that more first-borns than later-borns are likely to be scientists, and first-borns are over represented in parliament. They could have mentioned that as this evidence suggests birth-order can affect the job you do, it needs to be investigated, and once the study finds out whether differences exist the reasons can be investigated. The reference concerning the first-borns being more likely to become scientists is from 1874, so this may be outdated and not relevant in today’s society.

The introduction cites Sulloway’s (1996) family dynamics model. This says that the first-born child is more dominant and the youngest child is more extroverted. First-borns achieve dominance through being bigger due to being older, and having more parental resources invested in them if parental resources are low. To avoid conflict with elder siblings the later-borns learn to be agreeable with them, but to gain parental attention become rebellious. It is noted that studies finding results contrary to Sulloway have used between family designs, some are stated. However, some of the current research mentioned below support Sulloway’s findings and did not use within family designs.

Other research in this area suggests that birth-order does have an effect on personality. Basket (1985) asked adults to state their beliefs about a child based on their sibling status. The findings show that more positive ratings were given to oldest children than youngest or only children. It is suggested that these opinions might actually affect the child’s development causing them to self fulfil. Dixon et al (2008) investigated families with six siblings using questionnaires. They found an age affect, where the youngest three siblings were more extroverted than the older three. Paulhus et al (1999) investigated birth order effects on personality and achievement. He used a within family design that would be adopted by this study, with participants rating themselves and their siblings. The results show that first-borns are seen to achieve more and be conscientious while later-borns are seen as more rebellious and agreeable. Zweigenhaft (2002) tested Sulloway’s findings using a self report design from archives of a previous study. He found that later-borns are more likely to smoke marijuana than fist-borns and links it to them being more rebellious and extroverted. Jaffe (2004) investigated Sulloway’s ideas by testing sensation seeking, linked to extroversion. The results found no relationship between birth-order and sensation seeking.

This study’s introduction also cites Paulhus (1999), and states the findings fairly and as Paulhus did. It concentrates on Paulhus’ suggestion that between family designs are not appropriate to investigate this issue. His within family design removed the problem of different parental genetics and developmental environments that between family studies have. The simplicity of Paulhaus’ study is critiscised, so to gain the best findings this study uses the within subjects design, but a more complex questionnaire. Based on previous research with within family designs, the hypothesis that first-borns will be more dominant and later-borns more extroverted is justified.

When gathering participants, good measures were applied to avoid confounding the experiment. To avoid cultural differences confounding the results they must have lived in the United Kingdom for 17 years, (parenting styles in other cultures may differ and cause different results), and must not have studied psychology as this may have made them aware of the issue. The age gap could be no more than nine years as it would be a different society shaping personality, and not necessarily birth order effects within the home. It is good that there was only a difference of 2 first-borns and later-borns completing the study as this ensures both groups are represented equally in giving information.

A questionnaire design was used. It had two parts, seven questions associated with dominance and five questions associated with extroversion. Together, the twelve questions form the NEO-Five Factor Inventory extroversion scale. The questions were answered on a 5 point Likert scale ranging from strongly disagree to strongly agree. This assumes a positive ontology where people are categorised depending on the rating they give to each question, the results can be measured and applied to other people. A problem with this method is that reasons for the answers given cannot be explained. If any criteria that has been missed from the questions people cannot bring up, however, as the questions come from a reliable source that should not be an issue in this study. A better method may have been to use semi structured interviews, so all the relevant criteria could be assessed while allowing the participants to raise new issues. Times when a sibling had shown signs of dominance or extroversion could have been discussed to back up points. This would also allow non verbal cues to be assessed which may show what the participants feel about their sibling. A positive feature is that it keeps the study focussed on the point meaning this study has good construct validity as the questions are focussed on the aims of the study. The study has high internal validity as only the questions can influence the outcome, although it is relying on the person being truthful and not trying to look socially desirable.

Participants had to rate themselves and their siblings, then they were compared to whichever sibling is closest in age to them. Counterbalancing was used to avoid order effects. The reason given for studying the closest sibling in age is that, the larger the gap, the less the birth-order effects are evident. However, as long as they are within the nine year period it should not matter. If the youngest has three siblings to compete for attention with, their behaviour may have to be even more extroverted to gain attention than their elder siblings, and as the older sibling will be older by a bigger age gap he will be physically larger and even more dominant. A weakness is that the participants rate both themselves and their siblings. This can give a biased view of the non present sibling. An argument they could have had that day may affect the ratings that the other sibling is given. The findings would be more valid if the sibling was present to also rate both people as a cross reference of the results.

The results were analysed using one-sample t-tests. They show that first-borns are significantly more dominant and later-borns are significantly more extroverted. The results are strong as they are within the 5% error allowance and support previous findings. On the evidence of the data, the decision to accept the hypothesis was correct. Additionally the size of age gap and gender were not found to affect the results. A post hoc analysis found that there was no difference in how participants rated themselves and their sibling for extroversion, but they are more likely to rate themselves as more dominant than their siblings. This is a very strong result as it is significant to within 1% meaning the conclusions drawn are valid. Although the results support the hypothesis, they are not presented in a clear way. It talks about t-tests then jumps to a Spearman’s result without mentioning they had done a correlation, then jumped back to t-tests. There was no graph or a table which would have made the results clearer. It states that a post hoc analysis was conducted but fails to state which test was used.

The conclusion that birth-order affects personality development is valid as the results show this. They rule out possible confounding factors of the study which are gender and size of age difference, as no significant results were found for these. This is a good point that is supported by the results and adds to the validity of the study. The findings are within the theoretical framework, as they support Paulhus’ (1999) findings, who used a within family design to investigate this topic. They also support Sulloway’s family dynamics model. These results support all but one of the current studies previously mentioned, even those not using a within family design. Additionally they support Dixon et al’s (2008) findings that there were no effects for gender. However, Jaffe (2004) found the opposite results, that there was no relationship between birth order and sensation seeking (linked to extroversion). Jaffe also found a gender difference, with females rating higher than males for sensation seeking. This makes the gender findings inconclusive overall.

It then goes on to justify the within family design method as important for reasons such as reducing socioeconomic differences. They claim that their significant results are due to the within family design and other studies’ non significant results are due to using between family designs, however, they cannot be sure that that either design is the best or worst method. Third party ratings, as in other studies may be less prone to bias and therefore more accurate than the within family design meaning the non significant results are closer to the truth. They do not expand enough on the practical implications of their findings.

Sufficient limitations are discussed. They acknowledge that people act differently in different situations and cite this as a limitation of the study, as they only look at the family context. This is a good criticism as the study only looks at a small part of their personality. They mention that they did not investigate biological reasons for the personality difference, and suggest this as a further study as well as attempting to link in an evolutionary reason. Other further research suggested was to get getting a sibship size greater than three to rate each other then compare all three to incorporate self reports and third person reports. It is discussed that social desirability can affect the answers given in self reports. However, there is a poor attempt to argue this is not a limitation. They state there is ‘substantial evidence’ that self reports give adequate results but do not cite any. They use Sulloway’s dissproved prediction that people rate themselves as extroverted to look socially desirable to attempt to back the point up, however that is only Sulloway’s opinion and it is not undesirable to be dominant.

Overall this is a good study, with results that corroborate other theories. It used a different method in a different context than other studies and found significant results. This method is perhaps more appropriate than the previous ones for this issue, making this study important. The design ensures the results come from people who know each other better, rather than people on the periphery. Future studies can consider this method to expand on these results. Sometimes the report did not flow and some of the points were poorly explained or unclear, mainly evident in the results and discussion. At times it put too much emphasis on the method used and not on the main results of the study. A large section of the discussion was defending the method, not talking about results. It discusses relevant limitations and reasonable future research is recommended. More research could be done on the reasons for birth-order effects, how to stop them, and results can be compared to studies in different cultures. In conclusion then it seems as though the order you were born may indeed have effected your resulting personality. Just one more thing to blame your parents for…

Leave A Comment

Please be polite. We appreciate that. Your email address will not be published and required fields are marked

This site uses Akismet to reduce spam. Learn how your comment data is processed.