Here’s the abstract from a peer-reviewed journal article that looks at perceptions of media bias:

Although claims of media bias are abundant, systematic and scientific investigations of potential biases are rare. The present study was an attempt to determine whether a perception of bias would be found in the headlines of lead or major stories taken from the Web sites of two major American news organizations, CNN and FOX News, during the final two months of the 2004 presidential campaign.

Significant perceptions of bias were found. Overall, headlines taken from CNN were rated as significantly more liberal than those taken from FOX News. Headlines taken from FOX News were rated as slightly on the liberal side of neutral. With CNN’s headlines slightly to the left of FOX News’, instructing participants that the headlines came from a particular source did not influence the results.Although the study by no means provides the definitive answer to whether major news organizations have biases, it indicates that perceptions of bias exist.

Wow. Fox News slightly to the left of neutral? Conventional wisdom says that Fox News is conservative and CNN is objective.

The study was published in the Spring 2007 issue of The Havard International Journal of Press/Politics.