Of course the media is biased, but this study doesn't prove it. Over at Pejmanesque I dropped a too-long comment, which I will recycle here:
The concept of the study is ingenious, but it has a fatal flaw, which, on a Sunday morning, I can only illustrate by tedious example:
The study simplifies the world by focussing on two types of (my term) "Newsmakers" (Dem and Rep Congressfolks) and one type of "Expert Authority" (think tanks). One distortion, not fatal in itself, is that the study overlooks other types of Expert Authority, such as universities and government agencies. The other problem, deadly when combined with the first, is that the study overlooks important Newsmakers, who may have a different pattern of citing Expert Authority than the Congressfolk do.
To really simplify, imagine that we look only at Ted Kennedy (for the Left, natch) and Tom DeLay. Let's suppose that Kennedy cites Harvard half the time and the Economic Policy Institute half the time in his speeches. DeLay, starting in 2001, cites Republican controlled Gov't Agencies half the time ("this Treasury Dept study shows we can afford this tax cut..."), and cites the Heritage Foundation the other half of the time.
Our hypothetical sample newspaper, "Fair and Balanced", dutifully reports each story in the format of "Kennedy said, citing X; Delay said, citing Y". For true balance, half the time they report DeLay's view first.
The result - in the course of one hundred stories Kennedy will cite the EPI fifty times, DeLay will cite the Heritage Foundation fifty times, and the newspaper will cite both institutions fifty times. After complex statistical crunching, the authors will conclude (despite having ignored all the cites of Harvard and the Gov't Agencies) that the EPI is left, the Heritage is right, and the paper is neutral. So far so good, and a clever plan it is!
Now, the problem - suppose we introduce a new Newsmaker, speaking for the White House - let's call him Bush. Bush may cite Expert Authority very differently from DeLay or Kennedy; in fact, since it is his Administration, let's assume he cites Government Agencies 100% of the time. Let's also assume Bush makes 50% of the news, to which Kennedy (the real voice of the Dem Party!) is quoted in response.
Now what happens over the course of one hundred stories at Fair and Balanced, which uses the same format described earlier? The Kennedy half of the stories results in fifty cites of the EPI; the fifty stories mentioning DeLay (as the balance to Kennedy) produce twenty-five cites of the Heritage; and the fifty stories which balance Bush with Kennedy produce zero cites for the Heritage.
Net result at Fair and Balanced - 50 EPI cites, 25 Heritage cites, and a liberal-leaning score!
That is not the answer we want for Fair and Balanced. Now, the time period for some of the papers studied is strictly within the Bush Admin (NY Times, for example), so I think the problem I am describing is fatal for those scores.
Some of the other media (CBS, IIRC) have scores based on stories that go back to the Clinton era, so the change of Admin would complicate my objection, but would tend to shift the scores to the right of the NY Times. My guess - we would need to calculate separate scores by date of Administration, and check to see if there was a big shift left when Bush took over. Such a shift, OTOH, might simply reflect an oppositional tendency in the media - they bash whoever is in the White House.
Well, I am not changing my mind about a liberal media, and I think this study is based on an ingenious idea, but I suspect that the authors may have gone a simplification too far.
UPDATE: Try this for a bit of symmetry - our friends on the left are able to take a couple of comments from Ari Fleischer and a videotape of a raised eyebrow to "prove" that the Bush Administration claimed that Iraq was an imminent threat, despite plenty of evidence to the contrary. OTOH, when conservatives point to numerous instances of odd reporting in the NY Times as evidence of liberal bias, it proves nothing. Where are the goalposts?
(And I am making up the bit about the eyebrow, BTW).