Professor Luke O'Neill

There's a correlation with, say, the third child or the youngest child getting into the arts.

You know, they're more creative.

They are inclined to be entrepreneurs and risk takers.

And that's because the parents have kind of the less strict and they get a bit more freedom and they're inclined to become much more creative.

And we all know being in the creative arts is notoriously badly paid.

And then, of course, there's plenty of jokes about the birth order.

So the eldest child will treat a group holiday like a military campaign.

They get spreadsheets and backup contingencies.

The middle child will argue both sides of a debate and not come to a conclusion.

The younger one will show up late to a family function and then become the centre of attention.

We love this sibling rivalry, don't we?

They were very famous comedians decades ago.

And Groucho said about his brother, my brother thinks he's a chicken.

He was making fun of him.

But then he showed he really did love him.

He said, we don't talk him out of it because we need the eggs.

So you can't beat a bit of humour when it comes to sibling rivalry.

But remember now, this study does have a serious side.

What it says is what happens to the infant and the young child in terms of infection can impact on their earning potential decades later.

So what that means is, may she vaccinate to protect them against these infections.