Border controls row: look at the numbers

I can't help feeling something is missing from the border controls debate. Ah, I know: proportion. The usual thing.

So, just in case anyone would like to pursue this, a few pointers to some numbers. The Home Office compiles a good set, easy to dig into. And without much effort you can look up:

a) The number of people who come through the border (the ones we know about), every quarter, for quite a few years now.

b) The number who are refused entry at border control and sent away, every quarter.

So you can divide one by the other to see what proportion of people are being picked up at border control and sent away.

That means you can see if this has changed and by how much. Amazing, eh?

This might give a rough sense of how many people have been missed because of the reported relaxation of border controls.

And it does indeed look to me as if this has changed a bit. Here's what the data looks like. (Note, it doesn't cover this summer but those numbers will be out before long.)

Chart: How many refusals per 100,000 admissions?

By simply eyeballing, you can possibly see evidence - let's be careful here and not rush to any conclusions - of what might be a relaxation during summer 2010 - the principle that's supposed to have been applied this summer and caused all the current political fuss.

It appears to have made a difference of about five people per 100,000, or 1,250 people in total.

Is 1,250 people a big number?

But you might also say 'well, looks to me as if from about Q3 2009 the rate of turning away fell by - oh, very roughly - ten people for every 100,000 admitted, or 100 per million.'

Multiply that up for about 25 million people coming in through the borders (wow!) per quarter and you get 2,500 people let in who you might previously have expected not to be, every three months. That's about 10,000 a year.

Is that a big number? Think hard about what you'd compare it with in order to assess it. Is it worth the money and the hassle? Are the dates at which the various changes happened significant? You decide.

Because it could be the case that it's not the period since Q3 2009 that was unusually low but the period 2007 to Q2 2009 that was unusually high.

So is the story about the summer queues? Or is the story what happened from 2009? Or is there some other explanation, who knows, to do with recession maybe?

The relevant tables seem to me to be this one from the admissions tables: 'Table ad.01.q: Passenger arrivals including EEA and Swiss nationals.' And this one from the removals tables: 'Table rv.01q: Non-asylum cases refused entry at port and subsequently removed.' Both are available from the Home Office.

Now I'd double-check with the Home Office or Office for National Statistics - preferably not the Home Office Press Office - that this is a reasonable way to look at the data. It's not going to be perfect, since it uses what are only probabilistic assumptions. There might also be something else going on within these stats that explains them.

But it's quite an interesting start, wouldn't you say?

A lot of big names are attached to this sort of stuff: computer-assisted journalism, data-driven journalism. But the thing that strikes me is that it's not part of routine journalism - and this seems to be for lack of being even interested in asking the question.

Because of course speculation about Theresa May's job is far more important than the effect of the policy, isn't it?

Michael Blastland is a journalist, author and creator of the BBC Radio 4 programme More or Less.