Diffusion Theory

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Research on the diffusion of innovations model began with the Bryce Ryan and Neal C. Gross investigation (1943) of the diffusion of hybrid seed corn among Iowa farmers. By 1941, about thirteen years after its release by agricultural researchers, this innovation was adopted by almost 100 percent of Iowa farmers. Ryan and Gross studied the relatively rapid diffusion of hybrid corn in two Iowa communities in order to understand this phenomenon so that it might be applied to the diffusion of other farm innovations. However the intellectual influence of the hybrid corn study reached far beyond the study of agricultural innovations and outside the rural sociology tradition of diffusion research that Ryan and Gross represented.

While there are examples of applications of diffusion theory in public health prior to 1960, particularly in immunization campaigns, it is mainly since the 1960s that the diffusion model has been applied in a wide variety of disciplines, including public health, education, communication, marketing, geography, sociology, and economics. From these diffusion studies in various disciplines have come a series of generalizations about the process through which an innovation (defined as an idea perceived by individuals) spreads through certain communication channels over time among the members of a social system. The innovations studied range from the rapid diffusion of the Internet to the nondiffusion of the Dvorak keyboard (to replace the less efficient QWERTY keyboard in typewriters and computers). The innovations that have been studied in diffusion have mainly been technological innovations.

In the 1960s the field of public health adapted the diffusion paradigm to speed the rate of adoption of family planning methods in Latin America, Africa, and Asia. At about the same time, public health professionals in the United States and other nations began to use the diffusion model for health education and other health promotion programs. Public health researchers began to conduct inquiries on how preventive health innovations spread among members of target audiences, and on the process through which new health programs and practices spread among organizations like public health or among health professionals.

Through these efforts, public health scholarship began to make more important contributions to an improved understanding of the diffusion model. Many of the public health innovations studied are preventive in naturean individual had to adopt a new idea at a certain time in order to avoid the likely occurrence of some unwanted health event at a later date. In most cases, this future outcome could not be predicted with certainty. Some heavy cigarette smokers, for instance, will not get lung cancer in future years. Also, the health consequences often lag behind the time of adoption of the preventive health innovation by many years. Adoption of "safe sex" practices at the time might have positive consequences (e.g., not becoming HIV [human immunodeficiency virus] positive) years later. Compared to an innovation like hybrid seed corn among Iowa farmers, preventive health innovations generally diffuse much more slowly and require much greater promotion to reach a comparable level of adoption.

Preventive innovations are perceived by their potential adopters as having a lower degree of relative advantage over current ideas and practices. One strategy sometimes utilized to overcome this problem is to stress other advantages of the preventive health innovation. For example, some family planning programs emphasize the improved sexual pleasure of a couple who does not have to worry about unwanted births. Nevertheless, from a diffusion viewpoint, preventive health innovations generally have a slower rate of adoption than do new ideas that are not preventive in nature.

A further distinctive aspect of some health innovations is that they are taboo; that is, they are perceived as extremely private and personal in nature because they deal with proscribed behavior. For example, in the first years of the AIDS (acquired immunodeficiency syndrome) epidemic in the United States, the broadcast media refused to carry advertisements for condoms, and newspapers would not print news stories in which expressions like "anal intercourse" were used. The means of HIV transmission was referred to euphemistically as "the transfer of bodily fluids." Communication about birth, death, sexual intercourse, and other bodily functions are considered taboo in many societies. Thus the communication of health innovations that deal with taboo topics face special difficulties.

Despite the preventive and taboo nature of many health innovations, the diffusion of health innovations has been found to share many common qualities with nonhealth innovations. For example, the five characteristics of innovations predict their rate of adoption, the adopters of health innovations can be usefully classified into adopter categories, and most individuals pass through the five stages in the innovation-decision process (knowledge, persuasion or attitude change, decision, implementation, and confirmation). And as with other innovations, mass media channels are more important in creating knowledge of an innovation than are interpersonal channels, which are relatively more important at the persuasion stage.

Further, as in the case of other innovations, most health innovations diffuse over time in the shape of a cumulative S-shaped curve. The crucial mechanism in this S-shaped diffusion process occurs at the point at which critical mass occurs, when enough individuals have adopted the innovation and its further rate of adoption becomes self-sustaining. Essentially, the diffusion process for all innovations consists of individuals talking to one another about the new idea, thus decreasing the perceived uncertainty of the innovation and giving it meaning through a process of social construction.

A number of investigations elevated the effectiveness of interventions designed to speed up the rate of adoption of a health innovation. For example, opinion leaders in a target audience may be given special training about an innovation, in order to speed up the diffusion process. An example of this process is the well-known North Karelia heart disease prevention project undertaken in England in the 1980s and early 1990s. The project identified and trained opinion leaders in the target audience in order to encourage others to discontinue smoking, begin exercising, and change their nutritional intake in order to lower their risk of heart disease.

Everett M. Rogers

(see also: Communication Theory; Diffusion and Adoption of Innovations; Family Planning Behavior; Health Promotion and Education )


Becker, M. H. (1970). "Factors Affecting Diffusion of Innovations Among Health Professionals." American Journal of Public Health 60:294305.

Freedman, R., and Takeshita, J. Y. (1969). Family Planning in Taiwan. Princeton, NJ: Princeton University Press.

Green, L. W. (1970). "Identifying and Overcoming Barriers to the Diffusion of Knowledge About Family Planning." Advances in Fertility Control 5:2129.

Mohr, L. B. (1969). "Determinants of Innovation in Organizations." American Political Science Review 63:111126.

Rogers, E. M. (1995). Diffusion of Innovations, 4th edition. New York: Free Press.

Ryan, B., and Gross, N. C. (1943). "The Diffusion of Hybrid Seed Corn in Two Iowa Communities." Rural Sociology 8:1524.