of content is good in all three cases" and advised Wikipedia users "Be aware that erroneous edits do occur, and check anything that seems outlandish with a second source. But the vast majority of Wikipedia is filled with valuable and accurate information." A 2008 paper in Reference Services Review compared nine Wikipedia entries on historical topics to their counterparts in Encyclopædia Britannica, The Dictionary of American History and American National Biography Online. The paper found that Wikipedia's entries had an overall accuracy rate of 80 percent, whereas the other encyclopedias had an accuracy rate of 95 to 96 percent. A 2010 study assessed the extent to which Wikipedia pages about the history of countries conformed to the site's policy of verifiability. It found that, in contradiction of this policy, many claims in these articles were not supported by citations, and that many of those that were, sourced to popular media and government websites rather than to academic journal articles. In April 2011, a study was published by Adam Brown of Brigham Young University in the journal PS Political Science & Politics which examined "thousands of Wikipedia articles about candidates, elections, and officeholders". The study found that while the information in these articles tended to be accurate, the articles examined contained many errors of omission. A 2012 study co-authored by Shane Greenstein examined a decade of Wikipedia articles on United States politics and found that the more contributors there were to a given article, the more neutral it tended to be, in line with a narrow interpretation of Linus's law. Reavley et al. (2012) compared the quality of articles on select mental health topics on Wikipedia with corresponding articles in Encyclopædia Britannica and a psychiatry textbook. They asked experts to rate article content with regard to accuracy, up-to-dateness, breadth of coverage, referencing and readability. Wikipedia scored highest on all criteria except readability, and the authors concluded that Wikipedia is as good as or better than Britannica and a standard textbook. A 2014 perspective piece in the New England Journal of Medicine examined Wikipedia pages about 22 prescription drugs to determine if they had been updated to include the most recent FDA safety warnings. It found that 41% of these pages were updated within two weeks after the warning, 23% were updated more than two weeks later, and the remaining 36% had not been updated to include the warning as of more