This chapter suggests a particular estimation process, based on the simple scenario approach, that can be developed in various ways. In its simplest size the uncertainty form, it provides a simple alternative to high, medium, and low scenarios defined in purely qualitative terms, explicitly linking a comparable scenario approach to full quantitative analysis via a simple quantitative interpretation of the scenarios.
Chapter 15 develops further key ideas underlying this chapter. In particular, the minimalist approach special case of the simple scenario approach provides a useful short cut, which also clarifies why a high, medium, and low qualitative approach is ineffective and inefficient. A key feature of the minimalist approach is using what we know about anchoring and other sources of bias to design them out in so far as this is feasible (e.g., choosing the most effective sequence of steps).
There is a large amount of literature on probability elicitation, for good reason. Much of it complements the approach suggested here, but some of it is contradicted by the discussion here. We hope sufficient detail has been provided to indicate which is which for those who wish to develop deep expertise in this area. We also hope those not concerned with the finer points of these arguments will feel comfortable applying the suggested approach.
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