What about wealth though?

The same definitional issues apply as with income. Are we talking about the differences in the average level of wealth between countries? Or is it the difference in the level of wealth between all the people on the planet?

Evidence from a regular report by Credit Suisse suggests that inequality on both measures is probably rising.

It's important to remember that wealth gains in recent decades of a small band of oligarchs in India, China and Russia relative to the rest of their countrymen and women have been astounding.

However, the quality of this cross-country comparison data is inevitably patchy given it has to be compiled and imputed from a vast range of diverse surveys and national accounts of variable reliability.

The trend of wealth inequality within countries is also disputed. For instance, the UK’s official survey shows a rather flat trend in wealth inequality in recent years, but researchers say such surveys are fatally flawed because they have don't do a very good job of capturing the vast riches of those at the very top.