Consensus information is an integrative part of our social lives. Whether we intentionally seek, or unthoughtfully attend to, information conveyed by mass media, we learn about, for example, what other people believe on various issues, how other people intend to cast their vote in a forthcoming election, how many experts urge us to purchase a speci®c commodity, or how many fellow consumers are already satis®ed with the use of a speci®c brand. Advertising and political communication frequently employ their persuasive campaigns on the basis of consensus information. From a social psychological perspective, to know what other people do or believe is an essential way to evaluate our own behaviour and attitudes. It has been long recognized that we turn to other people in order to verify or falsify our way of seeing the world (e.g., the social testing hypothesis of Festinger, 1950). The effect of consensus information on thinking and behaviour has been the focus of much social psychological research (see Hardin & Higgins, 1996). Since early research on conformity researchers have been interested in the degree to which people's attitudes and behaviour change under the in¯uence of varying levels of group size (Asch, 1951).