Why is data on grooming gangs so bad?

Tim Harford looks at some of the numbers in the news and in life. In this episode:

Why is the data on the ethnicity of grooming gangs of such poor quality?

Iran has apparently enriched uranium to 60%, but what does that number mean?

Adam Curtis’s latest series, Shifty, includes claims about Margaret Thatcher’s rise to power. We ask Sir John Curtice, polling king of election night, if they’re accurate.

And we ask an economist to explain why being pillaged by a Viking might be more lucrative than you’d imagine.

If you’ve seen a number in the news you think needs a stern look, email the team: moreorless@bbc.co.uk

More or Less is produced in partnership with the Open University.

Presenter: Tim Harford Reporter: Josephine Casserly Producers: Nicholas Barrett, Lizzy McNeill and David Verry Series producer: Tom Colls Production coordinator: Brenda Brown Sound Mix: Gareth Jones Editor: Richard Vadon