Wikipedia As a Data Source for Political Scientists: Accuracy and

ABSTRACT Inonly10years,Wikipediahasrisenfromobscuritytobecomethedominant infor-mation source for an entire generation. However, any visitor can edit any page onWikipe-dia, which hardly fosters confidence in its accuracy. In this article, I review thousands of Wikipediaarticlesaboutcandidates, elections, andofficeholders toassessboth theaccuracy and the thoroughness ofWikipedia’s coverage. I find thatWikipedia is almost always accu-ratewhenarelevantarticleexists,buterrorsofomissionareextremely frequent.Theseerrors of omission follow a predictable pattern.Wikipedia’s political coverage is often very good for recent or prominent topics but is lacking on older ormore obscure topics. Since its 2001 launch, Wikipedia has ballooned intothe world’s largest andmost popular reference site onthe Internet, eclipsing all competitors and puttingMicrosoft’s Encarta out of business entirely.1 Over 12million visitors have registered as volunteerWikipe-dia editors, with 150,000 active editors as ofMay 2010.2 This anon-ymous army has written every word on the site. At the same time, Wikipedia’s “crowd-sourcing ” approach to content creation pro-duces little confidence in its accuracy. One of Wikipedia’s more infamous scandals emerged in 2007, when prolific editor “Essjay” was found to have used false credentials to persuade other volun