Birth Order Influences the Formation of Long-Term Relationships

134 years since Francis Galton opened the birth order effects debate by observing that first-born sons and only sons were over-represented among English scientists, controversy has shrouded the issue such that we haven't quite gotten past whether birth order effects exist or not, let alone properly consider what they are or how they work.

Some scholars assert that the lack of conclusive evidence is due to methodological biases that may allow the researcher to find the result that he or she is looking for. So, in that sense, a researcher who seeks to confirm that the birth order effect exists may find it just as well as a researcher who seeks to disconfirm it might.

In Birth Order Effects in the Formation of Long-Term Relationships, Hartshorne, Salem-Hartshorne and Hartshorne seek to probe the birth effect in a manner that is as methodologically neutral as possible by simply determining if there are any correlations between the sharing of birth order and the likelihood of long-term relationship formation. Their results provide new research material that weighs in favour of the presence of birth order effects, though what drives this effect is still speculative.

By drawing on a sample of 900 US undergraduate students, the researchers found that people are more likely to form and be in long-term relationships, both friendly and romantic, if they share the same birth order than would be expected by chance. For instance, if I were a first-born child, the likelihood of me being close friends with another first-born child is higher than the likelihood of me being close friends with another second- or third-born child. This tendency was also found for romantic partners.

A second and similar web-based study was conducted which gathered responses from American participants (1,911) as well as participants from other parts of the world (713). Similar results were garnered. There was no significant difference detected between American and non-American respondents, suggesting that birth order effects on long-term relationships are not culturally variant.

The researchers also controlled for socioeconomic status and size of family, which is a progressive extension from other earlier studies. This eliminates the confounds of number of siblings one has and the socioeconomic class one belongs to, which can potentially influence one's development because it is a commonly known social phenomenon that wealthier and upper class families tend to have less offspring.

The authors surmise that birth order underlies personality traits and having the same birth order results in greater compatibility between personality types, leading to the formation of closer bonds in both friendships and romantic relationships.

Joshua K. Hartshorne, Nancy Salem-Hartshorne, and Timothy S. Hartshorne (2009). Birth Order Effects in the Formation of Long-Term Relationship Journal of Individual Psychology, 65 (2)

Is your best friend’s relationship advice/decision really the best for you?

When you have a relationship decision to make and you are at a loss as to which is your best available option, are your friends the ones you turn to? If your answer is yes, the following article may make you think twice in the future.

In the article Risk-Taking in Relationships: Difference in deciding for Oneself Versus for a Friend, the authors explored the idea that people tend to make riskier decisions or give riskier advice for their friends as opposed to when they are making one for themselves. Most existing research has so far focused on people making decisions for themselves. However, there is a lack of empirical research on decision making for others, which is a rather common situation in life. Examples include doctors making decisions for patients or politicians for their constituents. The authors decided that decision making in relationships would be a good starting point as participants are undergraduates, often with a good chance of encountering such relationship choices.

The first experiment asked 201 participants to fill in a questionnaire of 11 scenarios concerning real-life relationship problems. There were two options for each scenario, one that was risk-averse (e.g. a fun time with friends) and another that was risk-taking (e.g. potentially having a fun time with an attractive member of the opposite sex). All participants were grouped into 3 categories: (1) deciding for themselves, (2) deciding for a same-sex friend, and (3) advising a same sex friend. A risk-averse option receives a score of 0 and the alternative gets a score of 1. Therefore, if a participant chose the risk-taking option for all 11 situations, the score would be 11.

The results indicated that participants made riskier choices for their friends as opposed to for themselves. Moreover, results showed that there were no differences for the other-decision group and the other-advice group. However, a life impact analysis of the scenarios reveals that the impact of the situation on the person’s future life could influence the self-other difference. Therefore the second experiment was conducted to investigate this possibility.

In the second experiment, 20 scenarios were pre-rated with 12 chosen. Six of them were of the highest score for low life-impact and vice versa for the high impact scenarios. In general, the results concurred with the first experiment and the possibility of self-other difference from low or high impact scenarios was also confirmed. Participants were more risk-taking in low impact scenarios and more risk-averse in high impact scenarios. However, a non-linear analysis suggested that the conclusion might not be as straightforward. Evidence from the non-linear analysis indicated that not every low-impact scenario had participants choosing a more risk-taking decision for their friend. Self-other difference was non-existent or reversed in three of the six low-impact scenarios. For example, when asked if they would give their phone number to someone they just met at a party, 80% said they would but only 67% said they would tell their friend to do the same thing. Experiment 3 sought to find out why people take more risk in some scenarios when it comes to deciding for a friend while other scenarios produce a completely different set of results.

Before discussing Experiment 3 proper, a brief review of some literature to provide rational explanations will prove useful. People in general take into account more information when deciding for oneself than for others. One way to interpret this is that positive consequences are accounted for in oneself and others but people will also focus on the negative consequences only when deciding for themselves. The corollary is that there is a bias towards riskier decisions for one's friend since positive consequences weigh more in the decision-making process. Insofar as this explanation is true, we can reasonably expect self-other differences to disappear for high-impact scenarios, but what about the three low impact ones previously mentioned?

Each scenario (giving out a phone number, going to an out-of-town concert and buying a gold chain for a significant other) has the potential to produce negative outcomes. For example, going out of town for a concert may be dangerous if you find yourself too far from home with a person you've just met. As a consequence, there might be a chance that such considerations are not completely ignored despite the scenario being generally of a low impact.

There are generally two mechanisms by which negative information can be directed when making decisions. The first states that such information is not even brought to mind when deciding for others. If this is the case, explicitly stating the negative consequence would serve to negate the self-other difference. The second possibility is that the consequences, albeit being brought to mind, are given less weight.

Experiment 3 tested both versions. For this experiment, each scenario was provided with both positive and negative consequences for each risk option (same questionnaire as Experiment 2) for one group and no such consequential information for another group. If this inclusion eliminates the self-other difference, the first mechanism is supported. In addition, the conclusion of this experiment asked participants to provide reasons for their choices in the three low-impact scenarios with the largest self-other differences as in Experiment 2. If participants stated more negative reasons, it would mean they were aware but chose to ignore the consequences.

Results of Experiment 3 indicated that, regardless whether consequential information is present, the self-other difference is not removed for the low-impact scenarios. For the open-ended questions at the end, participants gave more negative reasons when deciding for themselves than for others. This raises an interesting question because it contradicts the prospect theory where people in general place more importance on losses than on gains. Maybe we place a different emphasis on our decisions when it comes to deciding for others.

With these results in mind, we definitely do know that people take more risks for their friends in decisions, at least with respect to relationships. So, before the next time you go banging on your friend’s door regarding your relationship problems, do bear in mind what their decision could mean to you.


Beisswanger, A., Stone, E., Hupp, J., & Allgaier, L. (2003). Risk Taking in Relationships: Differences in Deciding for Oneself Versus for a Friend Basic and Applied Social Psychology, 25 (2), 121-135 DOI: 10.1207/S15324834BASP2502_3