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We can predict which children will grow up to commit the most crime, claim the most welfare and have the worst health; all we need to knowing is a child’s mental and physical abilities at the age of 3, plus their family’s income. So says a study that tracked the lives of nearly 1000 people. But can it really be true?

What kind of mental and physical abilities did the researchers look at?

They did a battery of tests – examining intelligence, understanding of speech, self-control and dexterity, for example – and pooled the results to give an overall measure of “brain health” that correlated with a child’s outcomes in later life.

Are the effects on adult outcomes the result of nature or nurture?

The study didn’t address that issue, although the team’s previous work has. Rather than the causes, this time of Duke University in Durham, North Carolina, and her colleagues looked at correlations between various hallmarks of childhood deprivation and a , by tracking nearly 1000 New Zealanders for forty years. As well as crime, the outcomes included how many medicines people take and whether they smoke or are obese.

Does this mean they think being fat is comparable with being a criminal?

Moffitt’s team say they weren’t making moral judgements but were measuring behaviours that “saddle society with costs”.

How new are these findings – didn’t we already know some of this?

It’s no surprise that poor children often grow up into poor adults, nor that poverty is linked with crime. And research also shows that poorer people have worse health, partly because of unhealthy behaviours such as smoking. What is surprising, Moffitt says, is the extent to which a small fraction of society account for disproportionate economic burden. When the children who start off in about the bottom 20 per cent in terms of brain health reach 38 years old, they account for about 80 per cent of doctors’ prescriptions, and 80 per cent of crime.

Why does that idea sound familiar?

It’s sometimes known as the Pareto principle, after a 19th-century Italian who observed that often 80 per cent of effects stem from 20 per cent of sources. It’s seen in diverse fields – for instance in software programming, where most of the bugs are said to be in a small fraction of the code. Although the 80:20 ratio wasn’t true for all the behaviours measured in this study, it was for certain costly outcomes. So Moffitt’s team argue that government help for poor families saves money in the long run.

What can governments do?

Many things. Parenting classes teach the importance of talking and reading to children, and having consistent rules, for instance. Free nursery and preschool places also help children develop their language and numeracy skills. But all these things cost money.