Adler, a middle child, argued that firstborn children tended to be more neurotic than their younger siblings because they were “power-hungry conservatives” and constantly fighting for dominance and success. Middle children, on the other hand were more agreeable and open to new experiences, he claimed.
Adler’s birth-order theory made Freud, a firstborn child, furious, and apparently contributed to the two men going their separate professional ways.
Well, it appears that Freud may have had a point. For a new study on birth order, personality and intelligence — the largest one ever conducted — has found that where we fall in our family chronology has no meaningful effect on our personality or on IQ.
That’s right. Another popular pop-psychology topic for dinner parties — the idea that each of us fills a particular personality “niche” in our family based on the order in which we were born — seems to have been debunked.
Although the “family niche” idea is widely accepted by the general public, it has always been controversial among scientists, for research on the topic has been inconclusive. Among its strongest backers today are evolutionary psychologists, who hypothesize that siblings compete for their parents’ attention by filling particular roles (“dominating,” “parent-pleasing,” “rebellious”) within the family — roles greatly determined by birth order.
A different study design
For the current study, a team of researchers led by University of Illinois psychologist Brent Roberts analyzed data collected on the personality traits and intelligence of 377,000 high school students. This was the largest pool of people ever studied for this purpose.
The researchers also used a different kind of research design than that of past studies. They compared people from across families rather than from within families — a model that Roberts and his colleagues say is more accurate.
“[Within-family] studies often don’t measure the personality of each child individually,” said Rodica Damian, one of the study’s co-authors and an assistant professor of psychology at the University of Houston, in a released statement. “They just ask one child — usually the oldest, ‘Are you more conscientious than your siblings?’”
The researchers also controlled for several potentially confounding factors, such as the students’ age, gender and number of siblings, as well as family income. That last point is particularly important, because parents who are both wealthier and more educated tend to have fewer children. Their children have a much greater chance of being a first-born (a 50 percent chance in a two-child family versus a 20 percent chance in a five-child family). So, the personality and IQ traits attributed to first-born children in past studies may have more to do with a greater access to resources than with birth order.
The analysis of the data in the current study found that birth order was associated with some traits that fit the previous hypothesized claims. First-born children did tend to have, on average, a one-point IQ advantage over their younger siblings, for example. And they also tended to score slightly higher on the “dominance” aspect of extraversion.
But those correlations had magnitudes that were “remarkably small,” to the point of being meaningless, say the researchers.
“You’re not going to be able to sit two people down next to each other and see the differences between them,” stated Roberts. “It’s not noticeable by anybody.”
The analysis also found that first-borns tended to have some personality traits that did not fit the claims of previous studies. They were, on average, more agreeable and less neurotic than their siblings — although again, the correlations were so weak as to be insignificant.
The researchers also found that the factor that correlated most strongly with personality and intelligence was the socioeconomic status of the parents, followed by the number of children in the family.
“The message of this study is that birth order probably should not influence your parenting, because it’s not meaningfully related to your kid’s personality or IQ,” said Damian.
The study was funded by the National Institute on Aging and was published in the Journal of Research in Personality.