(Andrew Harrer/Bloomberg)

Now for something that will surprise not one bit of the mass of mainstream media critics out there. A study by the Pew Research Center’s Project for Excellence in Journalism has found that President Obama enjoyed a “surge” in positive coverage over the last week of his campaign against Mitt Romney.

From the study:

During this final week, from October 29 to November 5, positive stories about Obama (29%) outnumbered negative ones (19%) by 10 points. A week earlier, negative coverage of Obama had exceeded positive by 13 points. The final week of the campaign marked only the second time in which positive stories about Obama outnumbered negative dating back to late August.

So how did Romney fare during this period? Negative stories drubbed positive ones, according to the researchers, by a margin of 33 percent to 16 percent.

Not only did Obama edge Romney on the positive-negative front, he was also beating him on volume, kind of like a Multimedia Costco. During that final week, the president talled an 80 percent mark of news articles in which he had a “significant presence,” according to the study; Romney reached that level in just 62 percent of articles.

Tone completes the media win for Obama.

In the end, 20% of stories during the fall period [Aug. 27-Nov. 5] about Obama were favorable compared with 29% that were unfavorable (a gap of 9 points). For Romney, 15% of stories during this full period were favorable while 37% were unfavorable, a gap more than twice as large as Obama’s.

The study finds that the uptick in positive Obama coverage stemmed from horse-race considerations — the president’s slight but steady lead in certain polls, in other words, prompted favorable coverage of his slight but steady lead in certain polls. Talk about a nice, self-perpetuating news loop. Get a lead in the polls, get some media assistance in maintaining that lead.

That, anyhow, is the innocent explanation for things.