Any statistics coming out of China always carry a caveat: beware of the quality of the information given its source. The reasons for bias are well documented, such as a bureaucratic infrastructure that grew out of the need to meet growth quotas during the height of the planned economy era. Actually gathering the information is difficult also simply because there are a lot of people in China.
Another objection, albeit anecdotal: every ten years China conducts a national census. At first this struck me as an efficient process, given that local bureaus can rely on Neighborhood Committees (another holdover from the communist period, sort of the state-sanctioned equivalent of a community organization) to send people around to all of the homes within the neighborhood to gather detailed demographic information.
So alone I sit one Sunday afternoon minding my own business. A loud knock comes at the door – and behold, it is a demographer, one of the older neighbor ladies who has been tasked with surveying residents. I open the door, “Oh” – she says “You’re not from around here. So you’re renting?” We go through her list – she wants to know I.D. number (“Oh that’s right you people don’t have those”), marital status, education, employment, name, age, home address (“Are you sure Pie-uh-nee-ar (Pioneer) Road doesn’t have Chinese characters? I need to write Chinese characters.”) After collecting what she wants, she heads off, and I return to my previous engagement.
About an hour later she comes back – I open the door and she says “Oh. Oh yeah wait. I was here already. SORRY!” No worries – there are lots of buildings, and many Unit 202s here in sunny Bamboo-Park-New-Village.
Another hour passes, and she returns a third time. This time it’s “OHHH darn I’m wrong again. I’ve already talked to you. I’m sorry.”
If we assume that grandma-citizen-demographer was average, then it stands to reason that even something as basic as the census might have considerable upward bias, purely from being oversampled by a factor of three. And hereafter, Shanghai’s population suddenly triples. National planners develop ulcers. The world again is astounded by China’s rapid growth.