The radiolab story “It’s Alive” made vivid the claim of Geoffrey West and Luis Bettencourt that a city’s size determines how fast people walk in that city. West & Bettencourt have written that people earn more in large cities, waste less, file more patents, and commit more crimes — and that city size is the main determinant of all these things. The charming Cosma Shalizi has recently published a 15-page paper that rebuts them. From the abstract:
Re-analysis of the gross economic production and personal income for cities in the United States, however, shows that the data cannot distinguish between power laws and other functional forms … and that size predicts relatively little of the variation between cities. The striking appearance of scaling in previous work is largely artifact of using extensive quantities (city-wide totals) rather than intensive ones (per-capita rates).
(Sorry if that’s hard to read. Horizontal axis = log( city population ). Vertical axis = pedestrian speed in m/s, give or take a standard dev. Solid & dashed lines are two fits proposed by Bettencourt & West.

Radiolab got it wrong

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