The diffusion model focuses attention on the social process surrounding health communication interventions. Messages may not only persuade individuals directly, but also stimulate interpersonal discussion about health behavior change. Evaluations under this model could not rely on comparing individuals who varied in exposure to the health messages, but would need to compare social networks that were more and less likely to have diffused messages. The institutional diffusion path carries with it a different implication. The audience for the communication interventions may be decision makers who determine institutional policies, rather than individuals whose behavior(s) are of concern. Indeed, if individuals are the audience, this audience may be seen primarily as a constituency who can influence policy makers, rather than as individuals whose risk behavior is to be changed. Evaluations of health communication interventions whose major path to influence is through institutional action cannot be conducted by comparing individuals with more and less exposure to messages. The appropriate unit of analysis is the institutional catchment area, often a geographically or politically defined unit, such as a city or state.
One possible way to speed up the likelihood of an institutional response is through media advocacy, the strategic use of mass media in combination with community organizing to advance healthy public policies. The primary focus is on the role of news media, with secondary attention to the use of paid advertising (U.S. Department of Health and Human Services, 1988; Wallack et al., 1993; Wallack, 1994; Wallack and Dorfman, 1996; Wallack and Sciandra, 1990-91; Winett and Wallack, 1996; Wallack et al., 1999). Media advocacy seeks to raise the volume of voices for social change, and to shape the sound so that it resonates with social justice values that are the presumed basis of public health (Beauchamp, 1976; Mann, 1997). Media advocacy has been used by a wide range of grassroots community groups, public health