REUTERS/Benoit Tessier Thomas Piketty director of the Paris School of Economics (PSE) attends the inauguration of the school in Paris, February 22, 2007. 
FT economics editor Chris Giles says he has found serious errors in data used by Thomas Piketty in his best seller "Capitalism in the 21st Century" about growing inequality in the Western world.
"Some issues concern sourcing and definitional problems," Giles writes. "Some numbers appear simply to be constructed out of thin air."
He continues:
For example, once the FT cleaned up and simplified the data, the European numbers do not show any tendency towards rising wealth inequality after 1970. An independent specialist in measuring inequality shared the FT's concerns.
Giles says he noticed the discrepancies while researching an article on UK wealth distribution. While Piketty said the top 10% per cent of British people held 71%, the UK's Office for National Statistics said it was just 44%.
The alleged discrepancies are similar to ones that undermined the findings of Carmen Reinhart and Ken Rogoff in their study of debt levels and growth, Giles says.
Reached by the FT, Piketty responded that he'd used "a very diverse and heterogeneous set of data sources ... [on which] one needs to make a number of adjustments to the raw data sources."
Given the huge influence of Piketty and the popularity of his book, this is a big story that will get talked about a lot more.