Bias doesn't even have to be a conscious thing... it's pretty easy to articulate the issue.
In a "Representative sample" scientifically you try and get a sample that perfectly represents your population to get fair research.
Meanwhile, studies of journalists political leanings aren't so representative.
http://www.journalism.org/node/2304
Even if were were to assume nobody in the media was trying to spin anything to their point of view. Psyologically you would in fact expect people to spin things to their point of view, simply because they would have a very different basic reaction to a story to begin with.
For example, to use the other side of the coin, say a Pro Life reporter is reporting about the chick fil-a founders comments and the protests, his natural first reaction would be "So what, this is stupid" and such a thing would show through in his reporting and writing of the story... even if he goes way out of his way to even it out. (Which i'd suggest most reporters don't.)
Proof of this is actually shown in that most "Middle of the road" reporters are actually more liberal then they think... as mentioned in the article.
"The research from Weaver and his colleagues echoes the findings of a Pew Research Center survey from 2004 revealing that while the majority of journalists described themselves as moderate, they were clearly to the left of the public. One example was that journalists were considerably more willing to say that society should accept homosexuality than the average citizen was."
So most journalists view of "Moderate down the middle" Is actually middle left... meaning that when journalists aim to tell an unbiased story, they invariably end up telling a more middle left story, since that's what they think is moderate.
And this was 2002. Reporters got a bit less liberal then... who knows what the report is going to show when it's done... I think next year actually.
With Bush being Bush, I can only imagine it's shifted even more liberal.
