April 30, 2020 - 10:48am

It’s the last day of April, by which date Matt Hancock had pledged the NHS would be carrying out 100,000 tests a day. He has since rowed it back to suggest that they would have the capacity to carry out 100,000 tests a day. But that’s not what he originally said.

I thought now would be an appropriate time to share an(other) email I got off a lab worker at the start of this week:

Demand is relatively low and seems to be falling. My unreliable beer-mat maths suggest that, with current staffing and equipment, but without reagent limitations, the local lab could process at least 500% of current demand daily.

The reagent thing is not really an obstacle right now, it only influences the speed of analysis. There simply is not a huge amount to test at this moment. The testing capacity has become more widely distributed over more hospitals than it was just two weeks ago, but even taking account of this, demand seems not to be ramping up quite as expected.

- Anonymous

I don’t know why demand isn’t going up — optimistically, it could be because social distancing and lockdown has reduced infections, so fewer people are showing symptoms; pessimistically, it could be that the testing centres are widely spread out, and essentially impossible for many to get to, especially if they’re ill and don’t have a car. Likely it’s a mix of both.

Whatever the reason, my correspondent says: “Arbitrary testing targets will probably just cause illogical and possibly detrimental changes to the system that we could do without.”

Giving a specific target made the testing regime a hotbed for Goodhart’s law. We don’t actually care whether 100,000 people are tested rather than 97,000 or even 52,000; we do care whether all the people who should be tested are being tested, without having to get on a bus for an hour while infectious.

But now that’s the mark of whether the government has succeeded or failed. Political journalists are “watching the numbers carefully” to see if they make it, as though they’re seeing if they have the votes in parliament; and Hancock is encouraging Tory members to sign up for tests, presumably to help them get closer to the target.

This is silly. None of it matters. It was a bad idea on the government’s part to give this arbitrary target; it is unhelpful of journalists to concentrate on it as though it’s important. The key is whether people who need testing can be tested. Forget the 100,000.

Tom Chivers is a science writer. His second book, How to Read Numbers, is out now.