ISLAMABAD, Sep 22(ABC): Is it true that growing up with a sister or brother influences one’s personality as an adult? Some people may say yes and go so far as to explain how their siblings’ gender may have impacted their personalities. Researchers have also long attempted to answer this question.
Now, an expansive study of more than 80,000 people in nine countries has what appears to be the definitive answer.
Having a sibling of a different gender does not affect one’s adult personality.
Study principal investigator Dr. Julia M. Rohrer, personality psychologist and lecturer for the Department of Psychology at the University of Leipzig, told Medical News Today:
“To clarify — we are looking at personality in adulthood rather than childhood personality. This is important to clarify because it could be that sibling gender does have effects on personality while people still live with their siblings, but which fade out later in life.”
“What surprised me was how consistently we couldn’t detect any effects on personality. We disaggregated the data in all sorts of ways to check whether there were effects in individual data sets, or maybe for certain birth cohorts, or maybe only for firstborns, et cetera. But we really came up mostly empty-handed!”
The researchers work with survey responses from people in the United States, the United Kingdom, the Netherlands, Germany, Switzerland, Australia, Mexico, China, and Indonesia.
Co-author Dr. Anne Ardila Brenøe, a research associate in the Department of Economics at the University of Zurich, said to Medical News Today:
“Given my own prior work, I had expected that having an opposite-sex sibling would increase gender-typed personality. We don’t find any evidence of this, which was surprising to me.”
The study appears in Psychological Science.
Gender mixtures in families
Citing research on this topic going back to 1958, the authors write:
“A closer look at the studies reveals a number of potential problems, such as highly selective samples, a multitude of different outcome variables, and statistical evidence of unknown or weak strength.”
To help narrow the focus of their investigation considering the multitude of family sibling gender configurations, the researchers employed a concept from a 2018 study by Dr. Angela Cools and Prof. Eleonora Patacchini, which was used again by Dr. Brenøe in her study.
“Parents’ decision to have another child,” write the authors of the new study, “likely depends on the gender but also may depend on the personality of their current children. Thus, the ultimate sibling composition is not random. As a result, differences between people with a brother and people with a sister may exist even in the absence of causal effects of siblings’ gender. But when parents decide to have another child, the gender of that next younger sibling is essentially random.”
“This results in a natural experiment that allows for the estimation of causal effects of the next younger sibling’s gender: Differences between people with a next younger sister and people with a next younger brother can be attributed to the next younger sibling’s gender.”
Personality traits and sibling’s gender
The researchers looked for siblings’ influence on the Big Five traits — including openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism — as well as trust, patience, and locus of control, or the belief that one has control over what happens to them.
Based on the survey responses, the study found consistent gender differences between females and males. This allowed them to explore the question of sibling influence using what they call the “typical female personality index” as a marker by which to measure personality effects.
“Importantly, this index is not meant to be interpreted as an underlying personality trait (‘femininity’). Instead, it is simply an index with the highest weight on traits for which the largest gender differences were observed within the particular surveys,” the authors wrote.
Beyond personality
It is worth noting that the Cools and Patacchini study found, “Women with a younger brother earned about 7% less than women with a younger sister,” according to the new study.
Cools and Patacchini found that women who had a younger brother more often chose traditionally female career paths and that, says the new study, “their wages dropped more drastically when entering motherhood than women with a younger sister.”
