In an article published last week, FT economics editor Chris Giles wrote that figures underpinning the 696-page book contained unexplained statistical modifications, "cherry picking" of sources and transcription errors. He said the mistakes undermine Piketty's conclusion that wealth inequality in Europe and the U.S. is moving back toward levels last seen before World War I.

After correcting for the alleged errors, two of the book's "central findings — that wealth inequality has begun to rise over the past 30 years and that the U.S. obviously has a more unequal distribution of wealth than Europe — no longer seem to hold," according to Giles.

One "serious discrepancy" Giles said he found was in Piketty's data on Britain. While Piketty cited a figure showing the top 10 percent of its population held 71 percent of national wealth, a survey by the country's Office for National Statistics put the figure at 44 percent.

In his latest web posting, Piketty disputes that the book contains transcription errors and disagrees with the adjustments to the data proposed by Giles, most of which he calls "relatively minor."

"The FT corrections that are somewhat more important are based upon methodological choices that are quite debatable," Piketty said.