Bernie Sanders says a vast amount of wealth - $50 trillion - has moved from 90% of the population to the wealthiest Americans since the 1970s. The figure comes from a study by Carter Price, a senior mathematician at nonprofit research institute the RAND Corporation.

Tim Harford speaks to Carter to understand how he calculated his figures and what they really mean.

If you’ve seen a number in the news you think we should take a look at, email moreorless@bbc.co.uk

Presenter: Tim Harford Producer: Nicolas Barrett Series producer: Tom Colls Sound mix: Giles Aspen Editor: Richard Vadon