Just before this BBC podcast gets underway, here's something you may not know.

My name's Linda Davies and I Commission Podcasts for BBC Sounds.

As you'd expect, at the BBC we make podcasts of the very highest quality featuring the most knowledgeable

experts and genuinely engaging voices. What you may not know is that the BBC

makes podcasts about all kinds of things like pop stars,

poltergeist, cricket, and conspiracy theories and that's just a few examples.

If you'd like to discover something a little bit unexpected, find your next podcast over at BBC Sounds.

Hello and welcome to more or less on the BBC World Service.

I'm Tim Harford and we're your weekly guide to the numbers that define our world.

Last year we had to say goodbye to Hans Rosling, a great friend of the show who died last February.

Hans used data to explain how the world was changing and

often improving and he'd challenge people to examine their own preconceptions and ignorance.

One of his favourite tricks was to pose people multiple choice questions

to test their assumptions against reality, as he did with our own Ruth Alexander.

The most important vaccine is the well-established measles vaccines.

Now, what is the proportion of all one-year-olds in the world that have got the

measles vaccine? Is it two out of 10, 5 out of 10 or 8 out of 10? I'd say it's 5 in every 10 50 percent.

Half you think.

Okay.

You were wrong.

It's 83% to get vaccinated.

83%?

...