If I told a hard-nosed journalist that I saw a blimp hovering slightly west of downtown Dallas on Friday night, that journalist might be a little skeptical. Sure, the Mavericks were playing the Suns, but you can't see through the roof of American Airlines Center. Why send a blimp? A careful reporter wouldn't take my word for it. He'd check it out.
But, assuming he knew me to be a reliable source in the past, he wouldn't be completely negligent simply to take my word for it and report that a blimp was in the Dallas sky, or at least that some people had seen one. And the story would in fact be true. There was indeed a blimp over American Airlines Center on Friday night, as the game telecast confirmed.
But suppose I told the same journalist that I saw a flying saucer from outer space hovering in the same place. A mainstream reporter won't believe me at all. Unless he heard the same thing from a lot of other people, he probably wouldn't even look into the story and debunk my tale with the blimp explanation. He'd just think I was delusional.
Much--though by no means all--journalistic bias lies in reporters' assessments of what's likely to be true. Those assessments are based in part on experience with sources and in part on how the reporter understands the world. What do you believe about political motivations? What do you believe about the way the economy works? What do you believe about the likely behavior of U.S. soldiers in combat, or of business executives, or of the clergy, or of Republicans, or of Jews? What do you believe about human nature in general? About political institutions? About the corrupting influence of money? About the power of ideology? About the relative importance of genetics versus culture, nature versus nurture? About the prevalence or sustainability of discrimination? About the influence of violence on TV? About the effectiveness of conspiracies?
Journalists make such judgment calls all the time. So, in fact, does everyone. We can't make sense of the world, or evaluate new information, without some mental model of how things work.That's why audiences gravitate toward media that share their worldviews, and it's why journalists can be fair or accurate, but we can never be unbiased unless we treat every source, and every claim, as equally credible. Like most mainstream American reporters, I'm reluctant to believe in UFOs, apparitions of the Virgin Mary, Jewish plots, or a radio transmitter in George Bush's jacket. Call me biased, but these widely believed phenomena simply don't comport with either my life experience or with my mental model of how the world works.