Democratic presidential hopeful Bernie Sanders speaks at a Phoenix event in July. (Patrick Breen/The Arizona Republic via AP)

A couple of weeks ago, Margaret Sullivan, the New York Times public editor, took on the question of whether the Times was biased against Sen. Bernie Sanders (I-Vt.). Some readers had been complaining. She concluded:

Here’s my take: The Times has not ignored Mr. Sanders’s campaign, but it hasn’t always taken it very seriously. The tone of some stories is regrettably dismissive, even mocking at times. Some of that is focused on the candidate’s age, appearance and style, rather than what he has to say.

Here I will look more broadly at media coverage of the Democratic candidates. As in previous posts, I draw on data from the firm Crimson Hexagon, who tracks the volume of coverage and gauges its tone across thousands of outlets.

Below is a graph looking at the share of coverage received by Sanders, Hillary Clinton and Vice President Biden, who is not a declared presidential candidate — as a fraction of the coverage received by all the Democratic candidates (including Martin O’Malley and Jim Webb). I’ve smoothed out some of the daily ups and downs to capture the longer-term trend.

In early May, Clinton was clearly getting the vast majority of coverage. But that has declined over time, largely because coverage of Biden has increased amid speculation about whether he will get into the race. Sanders got an increasing amount of coverage through late May and June and has plateaued since then.

Does the fact that, until very recently, Clinton has gotten more coverage than Sanders reflect media “bias”? I’m not so sure. News coverage will always focus on front-running candidates more than underdogs. (Ask Jim Gilmore.) This appears to reflect, as Jonathan Ladd discusses here, what political scientist John Zaller calls the “rule of anticipated importance.” Clinton has anticipated importance because, by perhaps the key metric (endorsements), she is the dominant candidate in the race.

Of course, perhaps the “rule of anticipated importance” is itself a kind of bias.  The question then is whether it’s a problematic form of bias. All news coverage reflects judgments about what, or who, is important, but we would not label all news coverage with the pejorative “biased.”

In the case of Sanders and Clinton, I don’t think the volume of coverage reflects a problematic bias. Surely dominant candidates don’t deserve all the news coverage. But I don’t think that the volume of Sanders coverage has been “too low” — especially given his likely chances of winning the Democratic nomination — currently, 12 percent in the prediction markets. Indeed, if anything, you could make the case for the opposite: that Sanders is getting more coverage than he “should” based on his chances of winning, perhaps because the media’s framing the Democratic race as competitive makes it more interesting to readers.

(You might also ask: Should media coverage even be indexed to the candidate’s changes of winning? That’s another blog post, probably. But I think the answer is yes.)

What about the tone of coverage? Crimson Hexagon evaluates the overall tone of stories mentioning each candidate. In the graph below, I subtract the number of stories categorized as positive from the number categorized as negative for both Sanders and Clinton. (The remaining stories were categorized as “neutral.”) Thus, larger numbers equal more negative coverage.

This graph shows that, contradicting the complaints of Sanders supporters to the New York Times, the coverage of Clinton has actually been more negative than coverage of Sanders on almost every day from May 15 to Sept. 14. This comports with, for example, Nate Silver’s analysis, which also suggests that negative coverage of Clinton is common.

Meanwhile, Sanders has yet to face a similar level of scrutiny. I’d also note that coverage of Sanders is often focused on his successes, especially as judged by horse race metrics such as the size of his rallies. (A search for “Bernie Sanders rally” returns 432,000 hits in Google News.)

Of course, I wouldn’t suggest that coverage of Sanders is always fair. (Nor is coverage of Clinton, necessarily.) But these data do offer some comfort to Sanders supporters.