I saw [this question](https://skeptics.stackexchange.com/q/31156/28873) on another Stack Exchange site, and wondered, how do they even know that one person in China died from "air pollution"?

How do these studies that lump millions of people into categories know how to classify the deaths? Do they categorically assume that everyone with asthma that died was killed by air pollution? If so, wouldn't all such statistics be overstated from the start?