Media Bias Aids Democrats by About 8-10% Points

That is the claim in a book by political science and economics professor Tim Groseclose.  To non-liberals it is obvious that there is a liberal slant in the mainstream media--the titles of stories, the stories chosen to be reported on, the questions asked (and not asked), and so on belies the fact that there is significant bias (not to mention polls of journalists on which party they favor).  Liberals will often go to great lengths to deny the bias, since for many of them it's hard to see bias in a piece of journalism about which they wholeheartedly agree.

Groseclose not only supports the view that there is such bias with his research but goes on to make the claim (about which he says he was initially skeptical) that the evidence suggests the bias significantly skews voter results to the left by almost 8-10% (which is enough to tip most elections).  If the bias were eliminated, he says, the U.S. would look like Texas (on the PQ scale which he explains below).  As he remarks, "If you want to change elections, become a journalist not a professor."

He discusses his methodology in this video (he talks for about 35 minutes and then answers questions):