Did the number of people around the world living in extreme poverty fall by half a few weeks ago? That's one interpretation of newly released figures for purchasing power parity around the world. The figures compiled by the International Comparison Programme of the World Bank show that in a lot of poorer countries, things are cheaper than we had thought. One development think tank has suggested that if people in these countries can afford to buy more, fewer of them will fall under the World Bank's definition of extreme poverty. We take a look at the argument to see if it stacks up, and whether the World Bank should be lowering its estimates for global poverty in light of the new figures. This programme was first broadcast on the BBC World Service.