How is "middle class" defined in that classification? In the US, for instance, you'd need to earn at least, say, (picking a random number without wanting to st

How is "middle class" defined in that classification? In the US, for instance, you'd need to earn at least, say, (picking a random number without wanting to start arguments and well-it-depends-where-you-live threads) $35,000 a year to be 'middle class', whereas China's per capita income is still less than $2000.