In contrast, Messrs Kharas and Rogerson think the majority of the poor will be in fragile states in 2025.

ECONOMIST: Free exchange

By 2020, more than half of the world's middle class is expected to reside in Asia, compared with one-fourth in 2009, estimates Brookings Institution economist Homi Kharas.

WSJ: Loans Surge to Asia's Growing Middle Class

There is another explanation for the differences between them: Mr Sumner is describing the present-day situation and Messrs Kharas and Rogerson are forecasting what might happen in 2025.

ECONOMIST: Free exchange

He agrees with Messrs Kharas and Rogerson that, as middle-income countries take more people out of poverty, the proportion of poor people who live in poor countries must rise.

ECONOMIST: Free exchange

The calculations by Messrs Kharas and Rogerson, using IMF data, seem to imply there will be hardly any poor people left in India and Indonesia in a few years, which seems unlikely.

ECONOMIST: Free exchange