Daniel Terdiman. “Study: Wikipedia as accurate as Britannica”. December 15, 2005 – “For its study, Nature chose articles from both sites in a wide range of topics and sent them to what it called “relevant” field experts for peer review. The experts then compared the competing articles–one from each site on a given topic–side by side, but were not told which article came from which site. Nature got back 42 usable reviews from its field of experts.
In the end, the journal found just eight serious errors, such as general misunderstandings of vital concepts, in the articles. Of those, four came from each site. They did, however, discover a series of factual errors, omissions or misleading statements. All told, Wikipedia had 162 such problems, while Britannica had 123.
That averages out to 2.92 mistakes per article for Britannica and 3.86 for Wikipedia.
“An expert-led investigation carried out by Nature–the first to use peer review to compare Wikipedia and Britannica’s coverage of science,” the journal wrote, “suggests that such high-profile examples (like the Seigenthaler and Curry situations) are the exception rather than the rule.””