Somehow, we're not completely impressed. Dow Jones has issued a report on "how well the PR industry promotes itself" based on worldwide media coverage of PR firms in 2010. From all we can gather, though, it's largely a quantitative report—saying nothing, expressly, about the nature/quality of the coverage generated. Column inches, of course, do not necessarily equate to standing.
So, for whatever it's fully worth, "Hill & Knowlton and Frank Public Relations drew top media coverage volume for large and mid-size agencies, respectively." Dow Jones says its Insights analysis uses both "qualitative and quantitative media measurement metrics," and it's likely willing, even anxious, to provide qualitative insights to its listed firms for a fee. But when a headline refers to ranking PR coverage, then reports without further explanation, folks could get the wrong idea of what PR's about—meaningful reputation building.
We refer you to the Dow Jones release with its accompanying coverage charts. Dow Jones notes that it "eliminated news releases and media contact mentions."