Charges of media bias have been flying like a bloody banner on the campaign trail. Newt Gingrich excoriated the “elite media” in a richly applauded moment during one of the Republican debates. Rick Santorum chewed out a New York Times reporter. Mitt Romney said this month that he faces “an uphill battle” against the press in the general election.

Meanwhile, just about every new poll of public sentiment shows that confidence in the news media has hit a new low. Seventy-seven percent of those surveyed by the Pew Research Center in the fall said the media “tend to favor one side” compared with 53 percent who said so in 1985.

But have the media really become more biased? Or is this a case of perception trumping reality?

In fact, there’s little to suggest that over the past few decades news reporting has become more favorable to one party. That’s not to say researchers haven’t found bias in reporting. They have, but they don’t agree that one side is consistently favored or that this favoritism has been growing like a pernicious weed.

On the conservative side, the strongest case might have been made by Tim Groseclose, a political science and economics professor at the University of California at Los Angeles. Groseclose used a three-pronged test to quantify the “slant quotient” of news stories reported by dozens of media sources. He compared these ratings with a statistical analysis of the voting records of various national politicians. In his 2011 book, “Left Turn: How Liberal Bias Distorts the American Mind,” Groseclose concluded that most media organizations aligned with the views of liberal politicians. (Groseclose determined that The Washington Post’s “slant quotient” was less liberal than news coverage in the New York Times and Wall Street Journal.)

Even with conservative-leaning sources such as the Drudge Report and the Washington Times factored in, “the aggregate slant is leftward,” said Groseclose, who describes himself as a conservative.

But that’s not the end of the story. A “meta-analysis” of bias studies — that is, a study of studies — shows something different: When all is said and done, left-leaning reporting is balanced by reporting more favorable to conservatives. “The net effect is zero,” said David D’Alessio, a communications sciences professor at the University of Connecticut at Stamford.

D’Alessio drew his conclusion from reviewing 99 studies of campaign news coverage undertaken over six decades for his newly published work, “Media Bias in Presidential Election Coverage 1948-2008: Evaluation via Formal Measurement.” The research, he says, shows that news reporting tends to point toward the middle, “because that’s where the people are, and that’s where the [advertising] money is. . . . There’s nuance there, but when you add it all and subtract it down, you end up with nothing.”

So why the rise in the public’s perception of media bias? A few possibilities:

l  T he media landscape has changed.

There’s more media and more overtly partisan media outlets, too. The Internet has given rise to champions of the left — Huffington Post, Daily Kos, etc. — as well as more conservative organizations such as Drudge and Free Republic. This means your chance of running into “news” that seems biased has increased exponentially, elevating the impression that “bias” is pervasive throughout all parts of the media.