Simple Bass diffusion modified from Sterman Business Dynamics Ch9. Compare with the SI infectious disease model Insight 584, to which we added churn and duplicated it to model a 2 sided marketplace..

In this 2-sided market model -- take etsy for example --  the adoption rate of end users is also a factor of how many vendors the company has on-boarded.  You can control the impact on end user adoption via the Choice Impact Factor.

Conversely,  the rate at which vendors will be on-boarded is a factor of the perceived opportunity they have to sell their wares.  You can control the rate at which suppliers are on-boarded via the Opportunity Impact Factor.

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The issue is how to select and keep optometry students. The main theme is balance out expectations with reality especially when many students use optometry as a proxy for later entry into a medical course. The second problem is that the current entry demographic does not meet the needs in terms of culture and expected practice location

Model of growth from diffusion from John Morecroft's Strategic Modelling and Business Dynamics Book Ch6 p174-191. A discussion of a bigger model of People's Express is in http://bit.ly/HdaGy4 for a related You Tube video by John Morecroft on Reflections on System Dynamics and Strategy