This interesting study by researchers from University of Pennsylvania looked at how the topic, content, lenght, style and other characteristics of the news articles affect the likelihood of people sharing them.
"To make sense of these trends in “virality,” the Penn researchers tracked more than 7,500 articles published from August 2008 to February 2009. They assessed each article’s popularity after controlling for factors like the time of day it was published online, the section in which it appeared and how much promotion it received on the Web home page.
A random sample of 3,000 of these articles was rated by independent readers for qualities like providing practical value or being surprising. The researchers also used computer algorithms to track the ratio of emotional words in an article and to assess the relative positivity or negativity..
..More emotional stories were more likely to be e-mailed, the researchers found, and positive articles were shared more than negative ones. Longer articles generally did better than shorter articles, although Dr. Berger said that might just be because the longer articles were about more engaging topics. (The best way to test that, he said, would be for The Times to run shorter and longer versions of the same article that would be seen by different readers.)
..Surprising articles, like one about free-range chickens on the streets of New York, were also more likely to be e-mailed — which was a hardly a surprising discovery, of course. But the researchers also kept finding popular articles with a quality that went beyond surprise."
