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Measures of posts about a TV show (“Can’t wait for ‘The Walking Dead’ to start”) are just the tip of Twitter’s iceberg, Mr. Somosi said in an interview: “The full iceberg is the extent to which people are seeing those tweets.” For example, the 225,000 posts about the Sept. 26 episode of “Grey’s Anatomy” were seen by 2.8 million distinct Twitter accounts, according to Nielsen’s algorithms.

It is impossible to say how many of those users watched the show as a result of the posts, but previous research has found that Twitter activity sometimes spurs viewership. Twitter has made collaboration with the television industry a priority as it seeks to impress investors; the prospectus for its initial public offering, published Thursday, mentioned television 42 times.

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– http://www.nytimes.com/2013/10/07/business/media/nielsen-to-measure-twitter-chatter-about-tv.html?ref=todayspaper