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S-shaped curve for uptake of innovations

By Steve Draper,   Department of Psychology,   University of Glasgow.

It is often said that innovations or new practices are taken up in an S-shaped or sigmoid curve. That is, there are broadly three phases. First just a few take it up: early adopters, the first few percent, over a long slow initial period of low usage; the first low slope of slow increase, and low total use. The third phase is also a low slope and slow increase, but high total use: these are the last reluctant ones. The second, middle phase has a high slope of rapid increase.

This view is attributed to Everett M. Rogers, and is described in his textbook "Diffusion of Innovations" (1962; 4th edition dated 1995; The Free Press; New York) e.g. ch.1 p.11 fig.1-1.

In fact you will get a sigmoid curve for cumulative adoption if the underlying rate of new adopters (new adoption events) forms a normal distribution (and if there is no significant rate of people dropping the innovation).


Rogers also talks of pro-innovation bias: from the tendency to study only those innovations that in fact did spread and become ubiquitous. Clearly such cases are no guide to what determines uptake in general.

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