The only way to sort out cause and effect is to do a randomized trial, moving people around between neighborhoods and tracking their health over several years.

要想找出原因，唯一的方案就是进行随机实验，让人们住进不同的社区，并在几年内坚持跟踪他们的健康状况。

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Once enabled, the tracking protection would exist for all Web pages the user visits and would take effect each time they start a new browsing session.

一旦这个功能启用，追逐保护将存在于用户浏览的所有网页中，而且每次打开一个新浏览器会话都会起效。

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In effect, the sponsoring groups were crowd-sourcing study subjects to get a larger sampling more quickly, using self-tracking methods for faster research results.

实际上，活动的组织者通过这种方式利用群众的力量，从而在更短时间内获得更大的研究样本，并通过自我跟踪方法更快地获得研究成果。

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You need commercial methods of delivering information and tracking its effect on the clients.

ECONOMIST: Who needs democracy?

Thus any fund manager tracking the index must, in effect, lend more to the countries borrowing the most.

ECONOMIST: Argentina's debt restructuring

As we started tracking this data we discovered something surprising: the majority of ripple effect website failures are caused by online advertising services, whose ads either slow down page load times or, worse, can actually prevent the entire page from loading.

FORBES: Revenue Good, Outages Bad: Ad Servers Can Slow Your Site