They actually programmed a computer for catch phrases and semantic variations to identify positive/negative/neutral, which has the advantage of weeding out conscious or subconscious biases of the researcher but the disadvantage of applying mechanical rules and probably coming up with some screwy individual results.
Factually correct information can still be presented in a heavily biased way. Even a certain facial expression when reading a story can convey disdain or sarcasm without any way to objectively classify it as such. That's why most of the studies done on this issue fail. Having a program do the classification is a good thing in terms of objectivity, but it fails to take into account a lot of possible bias.
I don't have any issue with idiots like madcow spewing their nonsense. Anyone who tunes into her show knows what they're tuning into. My issue is with biased reporting masquerading as objective news reporting.
I think you'll find that a huge portion of the negative on Obama right now has to do with reporting on opinion polls. When they say, "Obama's approval rating has dipped for the third straight month" I assume that counts as a negative.
I'd certainly count that as a positive
