Did 'rock-star' French economist Thomas Piketty get his numbers wrong? His theories about rising inequality and the increasing importance of capital have been the talk of the economic and political worlds this year. And part of their power has been the massive amount of data Piketty has brought together to back them. But the Financial Times claims to have found significant problems with Piketty's data on wealth. Tim Harford examines the FT's claims and Thomas Piketty's response. This programme was first broadcast on the BBC World Service.