In the 1960s, marketing researcher Frank Bass developed what
was essentially an extended version of Ross’s model.[52] Unlike
Rogers’s descriptive analysis, Bass used his model to look at the
timescale of adoption as well as the overall shape. By thinking about
the way people might adopt innovations, Bass was able to make
predictions about the uptake of new technology. In Rogers’s curve,
innovators are responsible for the first 2.5 per cent of adoptions, with
everyone else in the remaining 97.5 per cent. These values are
somewhat arbitrary: because Rogers relied on a descriptive method,
he needed to know the full shape of the S-curve; it was only possible
to categorise people once an idea had been fully adopted. In
contrast, Bass could use the early shape of the adoption curve to
estimate the relative roles of innovators and everyone else, who he
called ‘imitators’. In a 1966 working paper, he predicted that new
colour television sales – then still rising – would peak in 1968.
‘Industry forecasts were much more optimistic than mine,’ Bass later
noted,[53] ‘and it was perhaps to be expected that my forecast would
not be well received.’ Bass’ prediction wasn’t popular, but it ended up
being much closer to reality. New sales indeed slowed then peaked,
just as the model suggested they would.
As well as looking at how interest plateaus, we can also examine
the early stages of adoption. When Everett Rogers published the S-
curve in the early 1960s, he suggested that a new idea had ‘taken off’
once 20–25 per cent of people had adopted it. ‘After that point, it is
probably impossible to stop the further diffusion of a new idea,’ he
argued, ‘even if one wishes to do so’. Based on outbreak dynamics,
we can come up with a more precise definition for this take-off point.
Specifically, we can work out when the number of new adoptions is
growing fastest. After this point, a lack of susceptible people will start
to slow the spread, causing the outbreak to eventually plateau. In
Ross’s simple model, the fastest growth occurs when just over 21 per
cent of the potential audience have adopted the idea. Remarkably,
this is the case regardless of how easily the innovation spreads.[54]
Ross’s mechanistic approach is useful because it shows us what
different types of happenings might look like in real life. Think about
how the VCR adoption curve compares with the home ownership