How do you prove that news is bias?

Certainly Fox news has a habit of explaining news in a way that a conservative is more likely to agree with, and CNN may be more likely to give the news in a way a liberal would prefer, but how do you actually prove bias? As long as the actual facts of the case are accurate, is it really bias? More important, what... show more Certainly Fox news has a habit of explaining news in a way that a conservative is more likely to agree with, and CNN may be more likely to give the news in a way a liberal would prefer, but how do you actually prove bias? As long as the actual facts of the case are accurate, is it really bias? More important, what standard do we use to prove something is bias, and how do we actually present this evidence? When talking about this issue with people, I find that more often than not, if a station reports on something in a way that goes against their belief system they call it bias, but if its something that follows their belief system its neutral and accurate... so I think my questions are valid, what is bias, and how do we prove bias?
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