"With the exception of Nairobi — insert joke here about Kenyans crushing everyone at the New York City Marathon — the fastest walking cities were from wealthy nations. The statistical analysis confirmed this general perception: two of the three strongest social predictors of walking speed were a country's G.D.P. and its purchasing power parity (the other was its individualism). Indeed, when Levine considered all his "pace of life" metrics, he found that pace of life was swifter in "economically productive countries" like Western Europe and Japan than in undeveloped countries."