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Hello and welcome to more or less, the show that stays alert for numbers in the news,

controls for statistical accuracy and saves lives.

Well, there's no evidence for the last one, but I'm announcing it as a stretch target

we plan to hit by the end of the month.

I'm Tim Harford.

This week, the R-rate is one of the most important numbers of the pandemic.

Except of course, it's not a rate.

I only said that to wind up the epidemiologists, they love some banter,

but then what is R?

And how is it estimated?

We'll also go back to the vexed topic of testing and ask what the government's been doing

and what they've been claiming and whether those two things add up.

That all important two-meter gap at the heart of social distancing measures.

Why two meters?

Where does that come from?

And is Vitamin D an underappreciated weapon in the fight against COVID-19?

But first, there's a critical number that's guiding the government's lockdown strategy.

It's called the reproduction number or more simply R.

It's a measure of how many people on average one infected person is passing the disease onto.

So if R is one, then an infected person will infect on average one other person.

If R is two, then an infected person will infect two other people on average.

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