2.1. Constructing an initial model
When approaching a new problem there are two techniques
which are commonly used. The Wrst assumes we
have some idea how the situation under investigation
works, construct a model, and using this model select the
attributes believed to contribute to the eVect under investigation.
An example of this approach to this type of problem
is given in [9]. The second approach assumes little
knowledge of the underlying mechanisms involved so we
look at all the probably relevant attributes and try to determine
those which have the most signiWcant eVect. This is
still in eVect the construction of an a priori model, but only
a very informal one. In this paper, we take the second
approach.