To get the raw numbers, I wrote a series of fairly simple computer programs to monitor changes to all major Politico articles at regular intervals. (Here is more detail than you probably care to know about the programs.) After three weeks and nearly 400 articles, I have my answer: about 3 percent of the time.

By the end of last week, 217 of the 382 articles (57 percent) tracked had been changed in some way. Because the program detects even the most trivial changes, like the deletion of superfluous white space, the vast majority of these changes were unremarkable. Amid hundreds of these trivial changes, however, we found 12 noteworthy alterations. That amounts to 3.1 percent of the articles we monitored…

Among the pool of articles we monitored, Politico issued just three corrections. One notified readers that Howard Kurtz did not publish the first report of a massage therapist’s sexual-harassment allegations against Al Gore in the Washington Post.* One regarded the participants in a recent climate meeting. And one acknowledged that the site misidentified the author of a letter to President Obama. On the other hand, Politico failed to acknowledge changes it made on roughly a dozen articles, depending on how you count it. (See our list of deletions, corrections, and changes to judge for yourself.) After we contacted Politico with our list of unacknowledged corrections, the site’s editors appended correction notices to most of the articles in question.*