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64 E. Norling et al.

Fig. 5.1 The exploration and
consolidation approach to
model development

What steps then should modellers who follow such an informal approach take to
ensure that their model is sufficiently consolidated to present to a wider audience?
Firstly, the modeller must have a clear purpose for their model, as described below.
Secondly, the modeller must be careful to identify the assumptions that are made
during the construction of the model. Thirdly, the modeller must maintain control of
the model whilst exploring different possibilities. And fourthly—and this is perhaps
the most difficult—the modeller must maintain an understanding of the model. The
following sections of this chapter discuss these points in more detail. Then there
is the all-important consolidation phase (which may proceed in parallel with the
former steps, rather than strictly sequentially), during which the modeller formalises
the model in order to ensure that the results are sound and meaningful. Figure 5.1
illustrates this approach to model building.

5.2 Knowing the Purpose of the Model

There are many possible purposes for constructing a model. Although some models
might be adapted for different purposes without too much difficulty, at any one
time, a model will benefit from having a clear purpose. One of the most common
criticisms of modelling papers (after a lack of significant consolidation) is that the
author has made a model but is unclear as to its purpose. This can be for several
reasons, such as: