Diffusion as a Social Process
Diffusion, understood as ‘the act of spreading something more widely’ is fundamentally about processes of change. It is unsurprising therefore that it is the subject of intense interest across a wide range of academic disciplines, many of which stress the extent to which the successful diffusion of ideas is a function of the relationships between people.
Perhaps the earliest tract on diffusion was The Laws of Imitation published in 1880 by French sociologist and lawyer Gabriel Tarde. His stated focus was 'to learn why, given one hundred different innovations conceived at the same time – innovations in the form of words, in mythological ideas, in industrial processes, etc. – ten will spread abroad while ninety will be forgotten'. Tarde was a pioneer of diffusion research; many of the observations he made were confirmed much later by the early diffusion researchers of the 1940s and 1950s. For example, he discovered that diffusion followed an s-shaped curve; that opinion leaders played a key role in the ‘take-off’ stage of the diffusion process; and that innovations were more likely to diffuse if they were similar to existing ideas.
Moreover, Tarde believed that 'invention and imitation are… the elementary social acts.' That is, diffusion is a social process and is based on interpersonal contact within and across social networks. Despite the important conclusions Tarde made, his work fell out of favour in the first half of the 20th century. And, it is only in the last few decades (partly as a result of the growth in interest in social networks) that his work has been ‘rediscovered’. Certainly though, his work is relevant in the areas of communication studies, social network theory, and research on collective behaviour, public opinion and influence, and the role of opinion leaders in the diffusion of innovation.
Tarde’s theory of diffusion as a social process was confirmed by Bryce Ryan and Neal Gross’s influential 1943 study of the diffusion of hybrid seed corn among Iowa farmers, usually cited as the first study of innovation diffusion. It laid the foundations for several aspects of later diffusion studies: it conceptualised diffusion as the adoption of ideas or practices by individuals, largely through imitation; it discovered that the adoption curve was s-shaped; it differentiated between mass and interpersonal communication channels and identified distinct stages in the diffusion process; and most importantly it highlighted the importance of interpersonal networks and ‘opinion leaders’ in the diffusion process.
A further significant development was the idea of a ‘two-step flow of communication’, hypothesised by Elihu Katz and Paul Lazarsfeld in their classic study in the 1950s. According to this, ideas flow from mass media to opinion leaders and then out via these leaders to the wider population. So, the first step is the dissemination of information (from media to opinion leaders) and the second step is the use or spread of interpersonal influence (from opinion leaders to other members of society). This two-step flow model was in direct contrast to the ‘hypodermic needle model’, which claimed that mass media had a direct impact and influence on the behaviours and actions of individuals. As Rogers put it: in his Diffusion of Innovation: “the mass media was perceived as a strong influence on behaviour change. The omnipotent media were pictured as conveying messages to atomised masses of individuals.”
Within the field of sociology, there later emerged a particular branch of study – sociometry – which sought to measure and quantify social relationships. These early pioneers laid the foundations to what became more commonly known as social network theory. The basic assumption here is that people are embedded in social relationships, so the diffusion of information (or an innovation) is shaped by the nature of those relationships. One of the most significant contributions was made by Mark Granovetter in his seminal piece on the ‘Strength of Weak Ties’, published in 1973. He argued that weak ties (acquaintances) rather than strong ties (of friends and family) acted as bridges between tightly knit social groups and therefore facilitated the transfer of information and the diffusion of innovations across those subgroups. He also claimed that weak ties were indispensable to individuals’ opportunities in the labour market, to their integration in various types of communities, and that they enabled forms of collective action. Granovetter was also one of the first to identify a threshold model of diffusion, whereby an individual’s adoption of a new behaviour is a function of the behaviour of others in the group or system. More recently Thomas Valente identified ‘low network threshold’ individuals as those who adopt before many others in their network adopt, and ‘high network threshold’ individuals that adopt only after most of their network has adopted.
While these studies have shed much light on the social processes involved in diffusion, a continuing limitation of the research is that it suffers from a pro-innovation bias. This may be because there are a range of methodological challenges around researching non-adoption and rejection of an innovation. As a result, far more is known about successful innovations that spread quickly than those that did not. Similarly, we know more about adoption than non-adoption. Now that we can model the spread of ideas within social networks, further research would do well to examine the motivations and reasons that people give for adoption of these innovations.
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