I think that I understand your concern now. Obviously you agree now that an ideal logistic model does not exponentially increase without end, rather after the mid point of adoption, there is an exponential decrease in the adoption rate ...



My model attempts to fit a logistic curve to the price history of bitcoin. Stretch your mind a bit. We agree that exponential growth cannot go on forever, but how does it end for bitcoin prices?

Rather than  model the population of bitcoin technology innovation adopters, I am modelling the population of bitcoin financial speculators who transfer fiat to bitcoin. My rationale is that motivation to buy and hold bitcoins spreads through the finite population of speculators in a manner which positively depends on the size of the already-convinced speculator population, and is limited by the amount of funds that speculators are willing to transfer from fiat to bitcoin at a given bitcoin price. The logistic model has only two parameters, the adoption period (X axis above) and the maximum population size (Y axis above). I guess at the latter, i.e. what is the maximum price that speculators will pay when every convincible speculator has been convinced to buy. And I determine the adoption period by fitting the curve to the historical bitcoin price data.

Because the bitcoin price series is subject to periodic bubbles and crashes, e.g. most recently in the form of dampened oscillations, my model only suggests a likely trend for any supposed maximum bitcoin price.

Here is the shared spreadsheet that contains the model, which can be viewed - or copied and edited ... https://docs.google.com/spreadsheet/ccc?key=0ArD8rjI3DD1WdGhDN3FBWFptTlZTREN0cFkxZ3JHTnc