"There are three complementary models of behavior change implicit in many public health communication campaigns. The individual effects model focuses on individuals as they improve their knowledge and attitudes and assumes that individual exposure to messages affects individual behavior. The social diffusion model focuses on the process of change among social groups. The institutional diffusion model focuses on the change in elite opinion, which is translated into institutional behavior, including policy changes, which in turn affect individual behavior. The models contrast the direct effects of seeing mass media materials... with the indirect effects of the social diffusion model, (wherein) discussion within a social network is stimulated by PSAs (public service announcements) or media coverage of an issue; that discussion may produce changed social norms about appropriate behavior, and affect the likelihood that each member of the social network will adopt the new behavior. In the institutional diffusion model, media coverage of an issue may operate through either one or both of two mechanisms. Media coverage may affect public norms that affect institutional behavior or policymaker actions, or media coverage may lead policymakers to think an issue an issue is important and requires action, regardless of whether public norms have actually changed."
- Prof. Robert C. Hornik  (2002, pp.14-15)
Public Health Communication: Evidence for Behavior Change