Counting Crowds: Results May Vary

How many people attended Jon Stewart's rally last weekend, or Glenn Beck's rally last summer? It depends on who you ask. Two crowd-counting experts explain the "gold standard" for measuring crowd size, and discuss why some rally organizers might disagree with the counts.

Source: http://www.npr.org/templates/story/story.php?storyId=131099075&ft=1&f=1007

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