>According to the data, whenever a city doubles in size, every measure of economic activity, from construction spending to the amount of bank deposits, increase

>According to the data, whenever a city doubles in size, every measure of economic activity, from construction spending to the amount of bank deposits, increases by approximately 15 percent per capita. It doesn't matter how big the city is; the law remains the same. "This remarkable equation is why people move to the big city," West says. "Because you can take the same person, and if you just move them to a city that’s twice as big, then all of a sudden they’ll do 15 percent more of everything that we can measure." Am I missing something or is this reasoning fallacious? Correlation is not causation, and here it kind of looks like selection bias. I very much suspect that more productive people are more likely to move to bigger cities in the first place. (That's all on the assumption that the first half of the paragraph is from data and the second half is a conclusion he's drawing from those data, which is how it reads to me.)