That kind of data would be useful. "42% of the stories on major news networks during the six months during the election were favorable to Republicans, 32% favorable to Democrats, and 26% covered both sides" would be useful type information. I made those figures up, of course, but that would be data.
I don't know how we would judge "favorableness" to one side or another. Or how we could control for the possibility that Republicans, for instance, simply do more things that make them look bad. I mean, if one Democrat is involved in a bribery scandal involving $100,000 found in his freezer - but 20 Republicans are involved in a bribery scandal involving multiple
millions of dollars shaken down from Indian casinos, and the media reports on both stories with equal time and interest - is that fair and balanced? Or is that false balance, slanted against Democrats?
I'd say it's the latter, because the Republican scandal is a fundamentally larger and more important one. So increased media coverage of the Republican scandal would be warranted in my view, but one could easily make the argument "bribery is bribery; the greater focus on Republicans doing it is proof that the media is biased against Republicans."
It'd be nice if the data didn't come from a non-profit organization with the goal of correcting conservative misinformation in the media, but from some reasonably unbiased source.
Additionally, I don't know how we would judge whether or not a source was biased. I mean, if the media really
is slanting the news in favor of conservatives and Republicans, any source that pointed that out would fall under your classification of a "biased source." If we're going to reject as biased every source that comes to a conclusion
other than "the media is balanced", then you're simply choosing your conclusion at the outset.
I'm not trying to weasel out of providing data. I'm simply trying to explain why the only polling done on this issue is usually about how journalists vote - that's a really simple kind of poll to do. The fundamentally false idea is that this translates into some kind of indication of pervasive media bias.