Drawing on its analysis of campaign media coverage, the Pew Research Center’s Project for Excellence in Journalism has created a package of tools that let you track the volume and tone of coverage for each candidate, and the volume and tone of the conversation in Twitter. The tools also provide a gateway to data from other sources about media and public interest in the campaign. Use the tools

http://features.journalism.org/campaign-2012-in-the-media/tone-of-news-coverage/

Of course, the question for us here is the methodology used: what do they count and how do they count it?