Goa, on India’s western coast, is famed for its endless beaches, plentiful prawns and high quality of life. Bihar, along the fertile Indo-Gangetic Plain in the north, has a less savoury reputation. It is thought of by many Indians as a land of deprivation and lawlessness. Neither stereotype is entirely accurate, but they hint at a deeper truth. In terms of economic development, the difference between Goa and Bihar is like that between southern Europe and sub-Saharan Africa.

If the two states were countries, Goa’s annual output per person would put it among upper middle-income economies; Bihar, by contrast, would still be years away from leaving the low-income category. The average Goan is 10 times richer than the average Bihari. That disparity is much more striking than in China, also a large emerging market, where the richest province has annual output five times higher than the poorest. America, that famous beacon of egalitarianism, has nothing on either Asian country. New York, the wealthiest state, is just over twice as rich as Mississippi, the poorest.