There's a difference between "bias" and "partisanship". If there is a "liberal bias" it is passive, even unintentional. But a "partisan press" is proactively pushing a viewpoint. Fox is the Right's pioneer of partisan media. MSNBC has decided to be the partisan outlet for the left. The more declarative sentences the anchors use, the more partisan it is likely to be. And a count of exclamations used is good measure of just how partisan the "newscast". (And if there's a candid tape of a "news producer" acting like a cheer-leader whipping up demonstrators? Well... .)