Let me address the binary question first. In the wealth inequality tables for the top 1 per cent and top 10 per cent in Capital in the 21st Century, there were 142 data points and I found problems with 114 of them. As a problem proportion, it comes in at a rather high 80 per cent.

That overstates the case because the problems we raised were of different magnitude. If you exclude France and Sweden (where the problems are objectively minor), the error rate comes down to 52 per cent. This is still high.

Just to be clear, the error rate results from the difficulty in presenting any long-run US data at all given the problems in the source material and the serious limitations outlined in the British data.

Does it matter?

The main criticism of the FT’s work from The Economist’s Ryan Avent, and the New York Times’ Justin Wolfers and Neil Irwin is that although the FT has found problems with Prof Piketty’s data, it does not really matter.

This is a question of judgment. There is no doubt that the data the FT has questioned relate to just six charts in Prof Piketty’s book, not his theory, nor his numbers on income distribution. Many others have commented on those.

My point is that if someone is claiming to have found a fundamental contradiction of capitalism, predicts the result is a rising share of wealth inequality, and uses apparent recent rises in recent wealth inequality as evidence that his theory is correct, those data lie at the core of the book’s argument.

That overstates the case because the problems we raised were of different magnitude. If you exclude France and Sweden (where the problems are objectively minor), the error rate comes down to 52 per cent. This is still high.

Just to be clear, the error rate results from the difficulty in presenting any long-run US data at all given the problems in the source material and the serious limitations outlined in the British data.

Does it matter?

The main criticism of the FT’s work from The Economist’s Ryan Avent, and the New York Times’ Justin Wolfers and Neil Irwin is that although the FT has found problems with Prof Piketty’s data, it does not really matter.

This is a question of judgment. There is no doubt that the data the FT has questioned relate to just six charts in Prof Piketty’s book, not his theory, nor his numbers on income distribution. Many others have commented on those.

My point is that if someone is claiming to have found a fundamental contradiction of capitalism, predicts the result is a rising share of wealth inequality, and uses apparent recent rises in recent wealth inequality as evidence that his theory is correct, those data lie at the core of the book’s argument.

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