Sibling rivalry is a time honoured tradition in most families.

Everyone knows the stereotypes. First-born kids are spoilt brats. Second-born kids are often overlooked. And third-born kids are attention starved delinquents.

Speaking from experience, I can confirm that second-born children are, indeed, the best. But it helps to be the girl amid two boys. Because, clearly, girls are just better, overall.

Anecdotal evidence aside, fresh evidence is in from the world of economics to help us finally settle the question. Drum roll, please.

And the winner is: first-borns.

That’s right. New findings from large scale population surveys reveal that not only are first-born children more intelligent, they have better personalities, are more likely to be employed, earn higher incomes and have better mental health.

But it’s not all roses. The stress of being so awesome also means first-borns have higher blood pressure and are more likely to be overweight. A small price to pay, perhaps, for their innate superiority.

Ok, let’s break it down.

These controversial findings are reported in a recent article for the American National Bureau of Economic Research by Sandra Black an economist at the University of Texas and a former member of President Obama’s Council of Economic Advisers.

This is no Mickey Mouse study, but the result of large scale and thorough economic research.

Economists have long characterised children as a consumption good. Parents have kids because they expect to derive some pleasure from having them. Of course, children also come with substantial price tags, both monetary and time, that must also be factored into the decision.

Unlike luxury holidays and cars, which people tend to buy more of when they get richer, parents tend to have fewer kids as incomes rise. How do we explain this? Turns out the thing parents demand more of as they get richer is not a higher number of kids, but a higher degree of “child quality”. We want smarter, more socially well adjusted and healthier kids the richer we become.

Fair enough. Who doesn’t want that?

But it turns out that raising smart, personable and healthy kids requires quite intense parental resources – ask any parent.

And the more kids we have, the less time and resources we have for each.

The results of these constraints are evident in child outcomes.

Black and her colleagues base their findings of first-born superiority on large scale data from Sweden and Norway of men aged between the ages of 18 and 20, who enlist in the military and are subjected to a raft of tests on intelligence and personality, along with noting their birth order.

Of the Norwegian men, the birth order effect on intelligence is “strong”.

“Later-born children have lower IQs, on average, and these differences are quite large,” writes Black.

How big? Well, on this study, first-borns are on average three IQ points smarter than secondborns. This difference in intelligence translates to a 2 per cent earnings premium when they get jobs as adults.

So, first-borns are both smarter and richer.

They also have better personalities, or “non-cognitive abilities”, as measured by on a test administered to the men by a certified psychologist. “An individual is given a higher score if he is considered to be emotionally stable, persistent, socially outgoing, willing to assume responsibility, and able to take initiative,” Black explains.

Perhaps due to their higher intelligence, or these superior social skills, first-borns are “significantly more likely” to be employed as top managers. Later born children are more likely to be self-employed.

Smarter, richer and natural born leaders. Take another bow first-borns.

But being so fabulous can take a toll on one’s health. First-borns are 3 per cent more likely to have high blood pressure than second-borns and 7 per cent more likely than fifthborns. They’re also 4 per cent more likely to be overweight than second-borns and 10 per cent more likely than fifth-borns.

However, first-borns are more likely to report better mental health.

Now, how do we explain such differences?

Black advances several possible explanations. First, it’s possible first-borns are superior in some biological sense. They are born of younger wombs or to stronger healthier mothers, whose bodies are not yet ravaged by the demands of caring for other children.

Or maybe it’s nurture. “First-born children have the full attention of parents, but as families grow the family environment is diluted and parental resources become scarcer.” On the upside, family incomes tend to be higher when raising later-born children.

Interactions between siblings may matter too. First-borns spend a crucial period alone, while younger siblings must compete for attention from the outset. While first-borns follow the rules, “later-borns – by having incentives to engage in investments aimed at differentiating themselves – become more sociable and unconventional in order to attract parental resources.”

Now, no one is denying that younger siblings are not wonderful individuals who contribute greatly to society.

We’re just, on average, not as smart, employable or personable as our older siblings.

But hey, we’re skinnier. And that’s got to count for something, surely?

The Age