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Prince William and Prince Harry Wedding of James Matthews and Pippa Middleton, St. Mark's Church, Englefield, United Kingdom, May 20, 2017.
Prince William and Prince Harry at the wedding of James Matthews and Pippa Middleton on May 20, 2017.

If you think your big brother is already insufferable, wait until he hears this.

First-born sons are 24% more likely to become a "top manager," such as a CEO, according to new academic research. One potential reason: They tend to score better on personality tests designed to suss out leadership ability.

Indignant younger brothers may take some comfort from the knowledge that they're more likely to branch out on their own. They are more likely to be "self-employed" -- a category that includes entrepreneurs -- according to the study, conducted by economists in Sweden and at the University of Texas.

The study, released last month by the National Bureau of Economic Research, examined the lives of hundreds of thousands of Swedish men, seeking to measure the effect of birth order on personality traits. Researchers compared birth records to military and employment records. One key piece of data -- and one reason the Swedish population was so attractive to researchers -- was a battery of psychological tests that 18-year-old Swedish men were required to take as military recruits; universal conscription didn't end there until 2010.

Previous studies have shown that first-born children tend to score higher on IQ tests and out-earn later siblings. But this latest study attempts to explain the role personality plays in the equation. Looking at the military's personality tests, researchers found first-born sons scored higher on average for traits such as emotional stability, persistence, outgoingness, and willingness to take on leadership positions.

Those leadership qualities appeared to pay dividends later in life. First-born sons were roughly 24% more likely to become top managers than second sons and 29% more likely than third-born sons.

One major limitation to the study: It didn't examine the effect of birth order on women, who weren't conscripted and therefore didn't all take the psychological tests. The researchers did look at one wrinkle involving women, but only as sisters: comparing younger sons whose older siblings were female to those whose older siblings were male.

When it came to personality, men with older sisters tended to behave more like first-born sons, showing greater leadership traits than those younger siblings with older brothers. (The men with older sisters were also more likely to be employed than those with big brothers.)

But those leadership qualities traits did not necessarily translate into the same occupational success as the first-born sons. The gender of an older sibling had no discernible effect on younger brothers' likelihood of reaching the corner office.