editing in the Wikipedia model, with emphasis on breaks in flow (from vandalism or substantial rewrites), showing the dynamic flow of material over time. From a sample of vandalism edits on the English Wikipedia during May 2003, they found that most such acts were repaired within minutes, summarizing: They also stated that "it is essentially impossible to find a crisp definition of vandalism". Lih (2004) compared articles before and after they were mentioned in the press, and found that externally referenced articles are of higher quality work. An informal assessment by the popular IT magazine PC Pro for its 2007 article "Wikipedia Uncovered" tested Wikipedia by introducing 10 errors that "varied between bleeding obvious and deftly subtle" into articles (the researchers later corrected the articles they had edited). Labeling the results "impressive" it noted that all but one was noted and fixed within the hour, and that "the Wikipedians' tools and know-how were just too much for our team." A second series of another 10 tests, using "far more subtle errors" and additional techniques to conceal their nature, met similar results: "despite our stealth attempts the vast majority... were discovered remarkably quickly... the ridiculously minor Jesse James error was corrected within a minute and a very slight change to Queen Anne's entry was put right within two minutes". Two of the latter series were not detected. The article concluded that "Wikipedia corrects the vast majority of errors within minutes, but if they're not spotted within the first day the chances... dwindle as you're then relying on someone to spot the errors while reading the article rather than reviewing the edits". A study in late 2007 systematically inserted inaccuracies into Wikipedia entries about the lives of philosophers. Depending on how exactly the data are interpreted, either one third or one half of the inaccuracies were corrected within 48 hours. A 2007 peer-reviewed study that measured the actual number of page views with damaged content stated: "42% of damage is repaired almost immediately, i.e., before it can confuse, offend, or mislead anyone. Nonetheless, there are still hundreds of millions of damaged views." Loc Vu-Quoc, professor for Mechanical and Aerospace Engineering at the University of Florida, stated in 2008 that "sometimes errors may go for years without being corrected as experts don't usually read Wikipedia articles in their own field to correct these errors". Susceptibility to bias Individual bias and the WikiScanner tool