Public Opinion Quarterly, Vol. 72, No. 4, Winter 2008, pp. 781–791 FALSE CONSENSUS GOES ONLINE IMPACT OF IDEOLOGICALLY HOMOGENEOUS GROUPS ON FALSE CONSENSUS MAGDALENA WOJCIESZAK Abstract This study analyzes survey data obtained from members of neo-Nazi and radical environmentalist discussion forums. It assesses the extent to which participants in homogeneous online groups exhibit false consensus, i.e., overestimate public support for their views, and whether the overestimation increases with increased online participation. Although the analyzed sample overestimates public support, the over- estimation is no greater than found with more conventional populations studied to date. However, false consensus among the neo-Nazis increases with their involvement in online groups, also controlling for extremism. Among the environmentalists, it is the extremism, not online participation that accounts for false consensus. Theoretical and practical implications of these findings are discussed. Decades of research have demonstrated that there is a close relation between people’s opinions and their perceptions of the public opinion climate (Wallen 1943; O’Gorman 1975, 1979; Taylor 1982). Those who dislike dark bread will tend to think that others also dislike it, and people who support space exploration will be inclined to believe that others also favor sending humans into outer space (Ross, Greene, and House 1977). This tendency to attribute one’s own sentiments to other people has been labeled false consensus effect, and seems to be widespread across issues and circumstances (Krueger and Clement 1994). Will radical ideologues active in homogeneous online groups also think that the public shares their sociopolitical perspectives? Will continued interactions with like-minded online communities exacerbate the degree to which partici- pants see public support for their views? These questions are theoretically and MAGDALENA WOJCIESZAK is with the Annenberg School for Communication at the University of Pennsylvania, 3620 Walnut Street, Philadelphia, PA 19104-6220, USA. The author would like to thank Dr. Michael Delli Carpini, Dr. Vincent Price, and Dr. Michael Hennessy from the Annen- berg School for Communication, as well as three anonymous reviewers and the editor. Address correspondence to Magdalena Wojcieszak; e-mail: magdalena@asc.upenn.edu. doi:10.1093/poq/nfn056 Advance Access publication November 25, 2008 C  The Author 2008. Published by Oxford University Press on behalf of the American Association for Public Opinion Research. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org