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Well, because it's really an interesting (China related and economy/economics related) topic let me say what I think and know about it now:
1.
we must know the medium instead of the mean
-- very true, very right. Many people don't make difference between the mean and the medium. They just think that there is only one "average". And this is a problem.
2. In China (and other places too) it's a regular statistical trick (or just stupidity) to mislead the population that the average income is very good (and, of course, we should thank the "great" leader for this, right?) The typical example would be the case where nearly every person in a given population lives on about 4000 yuan a month, but there is a small elite with incomes in the tens of thousands (it implies more than 20,000). The numerical average can mislead many people by suggesting that the average Chinese person earns something like "(30 000 + 4000)/2", i. e. 17000 yuan monthly!
And this is, of course, ridiculous because the real situation is that most of the population in China can only dream of a month salary of ¥17000 (~$ 2,388)!
3. If you compare Shanghai with Canada, you better to specify which Canada do you mean, because as we talked before, in every country the GDP per capita (and the GINI index) differs from place to place. For example, I guess, if you compare Shanghai with Toronto or with Montreal maybe the Shanghai's per capita will be less but if you compare it with some small towns like Milton (
https://en.wikipedia.org/wiki/Milton,_Ontario) or Saint-Hyacinthe (
https://en.wikipedia.org/wiki/Saint-Hyacinthe) then Shanghai is likely better (about GDP per capita). Of course, I am not sure if these examples are 100% correct but what is really correct is that in every country the level is different when you compare the places (like comparing the GDP per capita in Korla /库尔勒/ and the same in Wuxi (无锡) or in Wanning (万宁)). But, sometimes, some small/smaller places may surprise you: according to one statistical source the highest Chinese mainland GDP per capita (after Hongkong and Macao) is in Karamay (克拉玛依); of course it's not really surprising if you know that that's an oil-producing (and refining) center.