Wikipedia articles, and the absence of any study statistical analyses (e.g., reported confidence intervals for study results) has also been noted. In June 2006, Roy Rosenzweig, a professor specializing in American history, published a comparison of the Wikipedia biographies of 25 Americans to the corresponding biographies found on Encarta and American National Biography Online. He wrote that Wikipedia is "surprisingly accurate in reporting names, dates, and events in U.S. history" and described some of the errors as "widely held but inaccurate beliefs". However, he stated that Wikipedia often fails to distinguish important from trivial details, and does not provide the best references. He also complained about Wikipedia's lack of "persuasive analysis and interpretations, and clear and engaging prose". A web-based survey conducted from December 2005 to May 2006 by Larry Press, a professor of Information Systems at California State University at Dominguez Hills, assessed the "accuracy and completeness of Wikipedia articles". Fifty people accepted an invitation to assess an article. Of the fifty, seventy-six percent (76%) agreed or strongly agreed that the Wikipedia article was accurate, and forty-six percent (46%) agreed or strongly agreed that it was complete. Eighteen people compared the article they reviewed to the article on the same topic in the Encyclopædia Britannica. Opinions on accuracy were almost equal between the two encyclopedias (6 favoring Britannica, 7 favoring Wikipedia, 5 stating they were equal), and eleven of the eighteen (61%) found Wikipedia somewhat or substantially more complete, compared to seven of the eighteen (39%) for Britannica. The survey did not attempt a random selection of the participants, and it is not clear how the participants were invited. The German computing magazine c't performed a comparison of Brockhaus Multimedial, Microsoft Encarta, and the German Wikipedia in October 2004: Experts evaluated 66 articles in various fields. In overall score, Wikipedia was rated 3.6 out of 5 points (B-). A second test by c't in February 2007 used 150 search terms, of which 56 were closely evaluated, to compare four digital encyclopedias: Bertelsmann Enzyklopädie 2007, Brockhaus Multimedial premium 2007, Encarta 2007 Enzyklopädie and Wikipedia. It concluded: "We did not find more errors in the texts of the free encyclopedia than in those of its commercial competitors." Viewing Wikipedia as fitting the economists' definition of a perfectly competitive marketplace of ideas, George Bragues (University of Guelph-Humber), examined Wikipedia's articles on seven top Western philosophers: Aristotle, Plato, Immanuel Kant, René Descartes, Georg