My main interest is in studying the effectiveness of campaigns that are focused on improving the health of the public. Usually the messages are aimed at getting people to improve some health behavior. For example, campaigns are waged to get people to eat better (the "Five-A-Day" campaign is an example), exercise more often, or practice safer sex.
One of the more interesting developments in the area of health campaigns is identified as "social marketing." Social marketing uses theories and tools from psychology, communication, and marketing to develop campaigns for social change based on individual behavior. For more information check on the application of psychology to mass communication and marketing you might want to check out these sites: