With the popularity of Thomas Piketty’s book, Capital in the 21st Century, inequality has become central to the public debate over economic policy. Piketty, and much of this discussion, focuses on the sharp increases in the share of income and wealth going to the top 1 per cent, 0.1 per cent and 0.01 per cent of the population.

This is indeed a critical issue. Whatever the resolution of arguments over particular numbers, it is almost certain that the share of personal income going to the top 1 per cent of the population has risen by 10 percentage points over the past generation, and that the share of the bottom 90 per cent has fallen by a comparable amount.

The only groups that have seen faster income growth than the top 1 per cent are the top 0.1 per cent and top 0.01 per cent.