In my lecture notes, I write,
A goal of economic or any scientific training is to think logically and free of bias. Bias ties our conclusions to our prior beliefs, eliminating the need for study.
In a comment about a book, Megan McArdle eloquently expands beyond my conclusion, reaching a profound conclusion that bias affects the questions asked.
What bias does--in science, in media, in any situation where information is gathered--is affect what questions you ask…
Bias matters not because researchers* deliberately slant their stories, but because they are much more likely to interrogate the facts that contradict their ideological beliefs, than the ones that support them. When they come across an uncomfortable fact, they'll go out of their way to figure out why it isn't really true. When they come across a fact that confirms what they believe, they'll be more likely to accept it at face value.
*I substituted the word liberals with researchers to conform with the impact of bias that I am teaching students. I feel comfortable making this substitution because McArdle also writes, “I'm not claiming that liberals do this more than conservatives (I think that being human, they're equally prone to this phenomenon)…”