Before this BBC podcast kicks off, I'd like to tell you about some others you might enjoy.

My name's Will Wilkin and I Commission Music Podcast for the BBC.

It's a really cool job, but every day we get to tell the incredible stories behind songs,

moments and movements, stories of struggle and success, rises and falls, the funny, the ridiculous.

And the BBC's position, at the heart of British music

means we can tell those stories like no one else.

We were, are and always will be right there at the centre of the narrative.

So whether you want an insightful take on music right now

or a nostalgic deep dive into some of the most famous and infamous moments in music,

check out the music podcasts on BBC Sounds.

Hello and welcome to more or less. We're the show that tries to make the world add up.

And I'm Tim Harford. This week, we bring you the story of how two people who had never met in

person worked together to find out just how bad things were in Mexico City during the

first wave of the pandemic last spring. In mid-March 2020, Mexico announced its first

official COVID death. A few weeks later, in late May, the total official death toll in the country's

capital was around 1800.

But among data geeks, something didn't sit right.

What we could see in Mexico was testing was really low.

We had a very high fatality rate in Mexico, about 8% compared to 1% in the rest of the world.

Many tests were coming up positive.

This is Lorient Despegale, an economist by day, but by night, something of a data detective.

That high fatality rate wasn't because COVID was more dangerous in Mexico.

...