And since different cities have different weather patterns, he says, this natural experiment allowed them to ask: Does a rainy day in New York affect running in San Diego?

阿拉尔表示，由于不同的城市有不同的天气模式，自然实验使研究人员产生这样的问题：纽约下雨会影响圣地亚哥的跑步活动吗？

"If the weather in New York causes changes in the running behavior in San Diego, it can really only be happening thru peer influences of the friends who live between New York and San Diego."

“如果纽约的天气可以改变圣地亚哥的跑步行为，这只能通过居住在纽约和圣地亚哥的朋友之间的同伴影响产生。”

And that is exactly what he and his colleague saw: that the behavior of one city's runners could indeed affect the behavior of runners in another socially connected city. The study is in the journal Nature Communications.

这就是阿拉尔和同事们得出的结论：一个城市跑步者的行为可能的确会影响与其有社交联系的另一个城市跑步者的行为。这项研究结果发表在《自然通讯》期刊上。

A few caveats: women tended to be influenced more by the female runners in their networks. And less active runners tended to influence more active runners to run more, but not so much the other way around. Still, this could be valuable intel for health professionals.

几点说明：女性更容易受其社交圈中的女性跑步者的影响。活跃度低的跑步者会令活跃度高的跑步者增加跑步距离，但后者对前者的影响却不太多。不过，这对健康专家来说可能仍是个有价值的情报。

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