Risk Analysis, Vol. 21, No. 3, 2001 467 0272-4332/01/0600-0467$16.00/1 © 2001 Society for Risk Analysis Source Credibility in Environmental Health–Risk Controversies: Application of Meyer’s Credibility Index Katherine A. McComas 1 * and Craig W. Trumbo 2 This article applies an existing five-item index for measuring source credibility in the context of environmental health–risk controversy. Survey data were gathered in five upstate New York communities facing environmental health–risk issues. Analysis of the five case studies and a combined dataset (N = 870) show that the credibility index was consistently reliable across all applications. Use of the resulting index is demonstrated through a comparison of the credibility of the New York State Department of Health (active in each case), the indus- tries associated with each case, and the newspaper providing coverage of each case. The cred- ibility index was used to predict risk judgments in a structural equation model. Overall, the analysis demonstrated that the credibility index performed consistently well across the five cases and illuminated important differences in each. As such, the index should be a useful ad- dition to many environmental health and risk communication studies. KEY WORDS: Risk communication; credibility; trust; risk perception; risk judgment 1. INTRODUCTION Regardless of context, source credibility is a key concern in communication efforts, but perhaps no- where is it such an important concern, in terms of af- fecting the welfare of individuals, as in public health and risk communication. Consider, for instance, some of the challenges facing U.S. health agencies, among them a widely documented decrease in confi- dence in American institutions responsible for man- aging risks. (1,2) A corollary may be seen in the growing concern among individuals about risks to their health and safety. (3) Although common sense would indicate that se- curing trust in the systems of environmental risk management is essential, some observers note that trust has been largely underappreciated in risk man- agement efforts. (3) Recent research suggests, how- ever, a growing recognition of the importance of trust and credibility to these efforts. (4–8) Indeed, some of this research has sparked controversy over prece- dents and approaches to measuring trust and credi- bility in risk communication, (9,10) culminating with the suggestion that a “broadened discussion” of the role of trust and credibility in risk management and risk communication is warranted. (10) One way to contribute to this discussion is to of- fer an additional, largely absent, perspective drawn from mainstream communication research. It is be- lieved that much of the recent risk communication re- search misses an opportunity to build from prece- dents available from mainstream communication outlets. Although not wanting to detract from the merit of current risk communication research being published on credibility and trust, it is believed that verifying the usefulness of established credibility in- dices, geared to measure the “believability” of the source, could significantly advance efforts to under- 1 Department of Communication, University of Maryland, College Park, MD. 2 School of Journalism, University of Missouri, Columbia, MO. *Address correspondence to Katherine A. McComas, University of Maryland, Department of Communication, 2104 Skinner Building, College Park, MD 20742-7635; mccomas@wam.umd.edu.