Health Communication, 23: 191–201, 2008 Copyright © Taylor & Francis Group, LLC ISSN: 1041-0236 print / 1532-7027 online DOI: 10.1080/10410230701808327 Subjective Knowledge and Fear Appeal Effectiveness: Implications for Message Design Robin L. Nabi Department of Communication University of California, Santa Barbara David Roskos-Ewoldsen Department of Psychology University of Alabama Francesca Dillman Carpentier School of Journalism and Mass Communication University of North Carolina at Chapel Hill This research investigates the role of perceived health knowledge on the effectiveness of fear-based persuasive appeals. Undergraduates (N = 263) read a strong fear, weak fear, or efficacy-only message encouraging breast or testicular self-examination. As expected, results indicated that men high in subjective knowledge were less reactant and more persuaded by the efficacy-only message whereas those low in subjective knowledge did not evidence this pattern. Contrary to expectation, women high in subjective knowledge had comparable reactions to each of the 3 messages. Implications for fear appeal theory and message design are discussed. Over 50 years of fear appeal research still leaves us uncer- tain as to the conditions under which fear might effectively lead to adaptive attitude and behavior change. Theoret- ical emphasis has been placed on the relative weighting of threat and efficacy perceptions to understand adaptive versus maladaptive action (e.g., Rogers, 1975; Witte, 1992), and although these perceptions are clearly important for the evocation of fear and potential responses (Floyd, Prentice- Dunn, & Rogers, 2000), no fear appeal model based solely on these concepts is conclusively supported by empir- ical research (Eagly & Chaiken, 1993; Mongeau, 1998; Roskos-Ewoldsen, Yu, & Rhodes, 2004; Witte & Allen, 2000). Consequently, we are left with rather general guid- ance as to how to best construct fear appeal messages for maximum effectiveness. Based on the extant literature, a fear appeal should contain threat and efficacy information sufficient to both Correspondence should be addressed to Robin L. Nabi, Department of Communication, 5838 Ellison Hall, University of California, Santa Barbara, CA 93106. E-mail: nabi@comm.ucsb.edu evoke fear and inform about adaptive behavioral responses (Rogers, 1975; Witte, 1992). This approach, although logical, seems to assume that the audience is either unaware of the threat, ignorant of effective responses, or both. How well, then, does this paradigm inform message design for audiences who see themselves as knowledgeable on one or both fronts? For example, if the audience seems aware of the threat, might it be just as effective, or even preferable, for the message to simply focus on the appropriate action? The goal of this research, then, is to examine how subjec- tive knowledge of a health threat impacts the effectiveness of differently designed fear appeal messages. A BRIEF HISTORY OF FEAR APPEAL RESEARCH Several reviews of past fear appeal research can be found in the existing literature (e.g., Leventhal, 1970; Mongeau, 1998; Witte, 1992), thus we offer only a brief overview