BASIC IDEA: One adaptation of the S-curve is known as the envelope S-curve, which takes into consideration successive generations of technologies that provide the same benefits. The term "envelope" refers to the curve that connects the tangents of the successive individual S-shaped curves.
PROCEDURE: Start by plotting the growth curves for successive generations of a technology. Try connecting the tangents of these curves to form an "envelope" and base the forecast on the extrapolation of the envelope curve.
EXAMPLE: In the graph below, the
sales data for 4k and 16k microprocessors is shown. The dotted line represents
the envelope for these two S-curves which can be used to forecast future generations
of microprocessors.
COMMENTS:
• There are several other functional forms that can be used for curve fitting, including exponential, double logarithmic, etc. A difficult part of this application is finding the curve that will best fit the available data.
• Very subjective and there is the probability of large errors
• Major problems, including:
• What is appropriate shape of the curve
• Which stage is variable in at the present
• What are lengths of the curve(s)
• Theoretical or practical (including social, economic, etc.) limits to the curve
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