Vivian B. Martin in Scientific American:
Groeling’s work is one of the few studies to quantify partisan bias in the media, a subject notoriously difficult for social scientists to research and discuss. These scientists work with theories such as the socalled hostile media effect to predict that ardent supporters of a cause will view media as slanted for the other side, and they have conducted hundreds of studies that have revealed imbalances in the ways journalists frame news on topics ranging from AIDS to the war in Iraq. But there is not a cohesive literature on media bias. Maxwell McCombs of the University of Texas at Austin, who pioneered agenda-setting theory, one of the leading paradigms on news media, says that a researcher would need a few years to make sense of existing data and develop an approach to study media bias. Like many scholars, McCombs sees “bias” as a loaded term, preferring to speak of journalists’ “predilections.”
“Scholars hate the word ‘bias’ because they feel like they’re entering the ideological fray,” says S. Robert Lichter, head of the Center for Media and Public Affairs (CMPA) at George Mason University, who prefers the term “tone.” Despite his efforts, Lichter himself got sucked into that fray. His content analysis of the transcripts of TV news broadcasts at the statement level is a respected and widely adopted methodology. This past summer, just as the view that journalists were going softer on Barack Obama than on John McCain was becoming widely accepted, CMPA issued a report showing that 72 percent of the statements in TV news reports about Obama in late spring and early summer were negative, whereas 57 percent of the statements about McCain were negative. When Fox News commentator Bill O’Reilly attacked Lichter’s method during a radio interview, saying it would embolden liberal bias, Lichter responded, “You can take all my studies or none of my studies”—an allusion to past uses of his work to support conservative views.