Boris Johnson has been hammered for using IQ to justify inequality.

You don’t need me to tell you in how many ways his attitude stinks.

But, even while you hate his attitude, you might be worrying that the statistics he quoted were arresting.

Here is what he said:

“Whatever you may think of the value of IQ tests, it is surely relevant to a conversation about equality that as many as 16 per cent of our species have an IQ below 85, while about 2 per cent… have an IQ above 130.”

So – cleverness seems incredibly rare. Only 2%! But not-so-cleverness seems alarmingly common. 16%.

So maybe inequality is an inevitable consequence of the unfortunate distribution of brain cells.

A lot of us are twits. Only a few of us are clever. So only a few get the wealth. It’s nobody’s fault but God’s.

But just in case nobody sets this statistical mischief straight for you, look at what BoJo has done.

At the clever end of the scale, he’s gone 30 points above 100.

But in the other direction, he’s only gone 15 points below 100.

So of course there are more below 85 than there are above 130.

Had he gone the SAME number of points down as up, and chosen to say how many people have an IQ below 70, guess what the number would be?

It would be 2%. The SAME as the number above 130.

This is because the distribution of IQ follows a ‘normal distribution’ – see the bell curve below.

What you need to know is that it is mirror-shaped. There are just as many of us with low IQs as there are with high IQs, and the pattern is THE SAME as you move further from the centre. It doesn’t matter which direction you go, up or down.

What BoJo should have said is:

“Whatever you may think of the value of IQ tests, it is surely relevant to a conversation about equality that just 2 per cent of our species have an IQ below 70, and just 2 per cent… have an IQ above 130.”

In other words, we’re all in this bell curve together.