- they use mean within countries (GNI per capita is GNI divided by population)
- middle-income is GNI per capita from 1036USD to 12615USD
By those definitions, the sentence isn't a very strong one because: (i) 1036USD is pretty low in most places, and (ii) (I'm guessing) the median incomes in those countries are lower than the mean incomes used to classify the countries, the means will be dragged up significantly by outliers like Carlos Slim.
- they use mean within countries (GNI per capita is GNI divided by population)
- middle-income is GNI per capita from 1036USD to 12615USD
By those definitions, the sentence isn't a very strong one because: (i) 1036USD is pretty low in most places, and (ii) (I'm guessing) the median incomes in those countries are lower than the mean incomes used to classify the countries, the means will be dragged up significantly by outliers like Carlos Slim.