DIFFUSION THEORIESare usually traced to Gabriel Tarde (1890) who
didn’t use the term diffusion, but was the first to
address the notions of adopters and the role of
social influence in adoption, as well as to identify
the S-shaped curve associated with the rate of an
innovation’s adoption. The formative empirical
work on innovation diffusion can be traced to
Bryce Ryan’s Iowa State University-based study of
hybrid corn seeds (published with Gross in 1943),
and Raymond Bowers’s (1937) study of the accept-
ance and use of ham radio sets. For more than two
decades following this pioneering work, the study
of innovation diffusion and particularly theory
development took place within the context of
rural sociology. This circumstance was a function
of a variety of forces, principal among which were
the location of rural sociologists in land grant
institutions charged with the dissemination of ag-
ricultural innovations to farmers (Hightower 1972)
and the communication and stimulation accorded
by the North Central Rural Sociology Committee’s
(a regional professional society) formation of a
special subcommittee to deal with the issue of
diffusion of agricultural innovations (Valente and
Rogers 1995, p. 254).
Most scholars agree that contemporary views
of innovation diffusion grew from hybrid corn
seeds; specifically the research on adoption done
by Bryce Ryan and Neal Gross (1943). These stud-
ies ultimately defined most of the issues that occu-
pied diffusion researchers and builders of innova-
tion diffusion theory for decades to come: the role
of social influence, the timing of adoptions, the
adoption process itself, and interactions among
adopter characteristics and perceived characteris-
tics of the innovation. From the middle 1940s
through the 1950s, rural sociologists vigorously
developed a body of empirical information on the
diffusion of innovations. Most of these studies
remained tied to agriculture and farming, and
focused on the diffusion of new crop management
systems, hybridizations, weed sprays, insect man-
agement strategies, chemical fertilizers, and ma-
chinery. A common criticism of the studies of this
era is that many of the studies seem to be almost
replications of the Ryan and Gross work, the main
difference among them being the specific innova-
tion studied. While it is true that these studies tend
to share a common methodology and linear con-
ception of diffusion, it is also true that they pro-
vide a strong foundation of empirical case studies.
Indeed, the replications that these studies repre-
sent substantially facilitated the later sophisticated
theoretical work initiated in the early 1960s (Rog-
ers 1962), and continued in the 1980s (Rogers
1983, 1988).
The 1960s marked the beginning of the de-
cline of the central role of rural sociologists in
innovation diffusion research. In large part this
was due to changes in the field of rural sociology,
but it also reflected the increasing involvement of
researchers from other disciplines, changing the
sheer proportion of rural sociologists working on
innovation diffusion. After more than two decades
of extensive research on the diffusion of agricul-
tural innovations, rural sociologists—like other
social scientists of the time—began to devote more
time to the study of social problems and the conse-
quences of technology. Indeed, Crane (1972) ar-
gued that around 1960 rural sociologists began to
believe that the critical questions about innovation
diffusion had already been answered. Although
the late 1960s saw rural sociologists launch a series
of diffusion studies on agricultural change in the
international arena (particularly Latin America,
Asia and Africa), by 1965 research on diffusion of
innovations was no longer dominated by members
of that field. Of course, innovation diffusion re-
search by rural sociologists has continued, includ-
ing studies of the impacts of technological innova-
tion diffusion, and diffusion of conservation prac-
tices and other ecologically-based innovations
(Fliegel 1993).
The infusion of researchers from many disci-
plines studying a variety of specific innovations
initiated the process of expanding the empirical
testing of innovation diffusion tenets. This began
with studies in education addressing the diffusion
of kindergartens and driver education classes in
the 1950s, as well as Richard Carlson’s (1965)
study of the diffusion of modern math. Another
major contribution came from the area of public
health. Elihu Katz, Herbert Menzel, and James
Coleman launched extensive studies of the diffu-
sion of a new drug (the antibiotic tetracycline);
first in a pilot study (Menzel and Katz 1955) and
then in studies of four Illinois cities (Coleman,
Menzel, and Katz 1957; Coleman, Katz, and Menzel
1966). This research greatly expanded knowledge
of interpersonal diffusion networks, and in par-
ticular its influence in adoption. Interestingly, as
Elihu Katz, M. L. Levine, and Harry Hamilton