• Your success in life may be influenced by your birth order, according to the economist Sandra E. Black.
  • Black points to research she and her colleagues have conducted that found that firstborns tend to be smarter, richer, and all-around more successful than their younger siblings.
  • That’s possibly because parents may be less invested in parenting with younger kids.
  • Still, other researchers have found minimal differences in intelligence and personality between firstborns and their siblings.

An article in the December issue of the National Bureau of Economics Research Reporter argues that firstborn children are likely to become smarter, more successful, and richer than their siblings.

One possible reason, it says, is that parents are in some ways less invested in parenting after the first go-round.

Sandra E. Black, a professor of economics at the University of Texas at Austin, highlighted studies she and her colleagues have conducted since 2004. Collectively, she wrote, their data suggests that birth order can explain differences in how well you do in school, how much money you earn, your intelligence, and your personality.

The science of birth order is a highly contentious topic – and not just among siblings. Academics can’t even agree on whether or how birth order shapes your success.

A 2015 review of studies, which included roughly 272,000 participants, found that differences in IQ and personality were so small as to be meaningless, pushing back on decades of other findings. In other words, it suggests that even if birth order is related to things like your job and your salary, it's not because firstborns are inherently smarter or, say, more outgoing.

"You're not going to be able to sit two people down next to each other and see the differences between them" if they have different birth orders, an author of the study, Brent Roberts, previously told Business Insider. "It's not noticeable by anybody."

Black, on the other hand, highlighted one paper she helped write that found that the difference in average IQ between firstborn and second-born children was about three points and that it translated to about a 2% difference in annual earnings. The data came from cognitive tests administered to young Norwegian men when they enlist in the military.

Firstborns are also more likely to be employed and work as top managers, Black's research found, while later-born children are more likely to be self-employed.

Black's research focused on personality traits as well. She found that later-born children received lower scores in those military tests on things like emotional stability, outgoingness, and willingness to take initiative.

Some research suggests that parents are less focused on schoolwork with later-born kids

So what might parents have to do with it? According to the research Black cites, parents spend less time discussing schoolwork with later-born kids.

A 2015 paper published in the Journal of Population Economics also found that a firstborn child was more likely to be punished by their parents for bad grades.

Black recently told Marketplace: "We find some evidence that suggests that parents invest differently with earlier-born children. We see that parents spend more time helping them with homework."

There is, however, a caveat.

"The problem is it's hard to distinguish whether that's the parents treating them differently, or the kids are different and the parents are just responding to it," Black said.

Punishment for bad grades isn't necessarily the best way to ensure future success. But assuming the parents are in fact treating their kids differently, these behaviors might suggest that parents simply don't have the same amount of time and energy to lavish on younger kids as they did on older kids.

One important note: Black writes that her data suggests that differences between firstborn kids and later-born kids are entirely due to the environment and not to biological factors. That is to say, every kid at least appears to come into the world with the same shot at success - it's what happens during childhood that makes the difference.