> In the final stretch of the campaign, nearly half (46%) of Obama’s coverage on Fox was negative, while just 6% was positive in tone. But MSNBC produced an even harsher narrative about the Republican in the race: 71% of Romney’s coverage was negative, versus 3% positive.

I am unsure it supports an argument for being the "most biased news network" outside of a specific election.

Also, it does not appear to account for reporting on a sitting president (who is also running for reelection) and will generate non-election news as well as election news versus a candidate who is not currently generating much news outside of their election.

There's going to be a number of mundane stories mentioning the president (i.e. bills being signed, travel, meetings, etc.) that are outside the scope of what's also being reported on a candidate.

The result is that any organization that is reporting on the president will inevitably mention the president in articles that are less biased, skewing the results comparison.