As mentioned in the introduction, choice models are referred to as disaggregate models. It means that the decision-maker is assumed to be an individual. In general, for most practical applications, this assumption is not restrictive. The concept of ``individual'' may easily been extended, depending on the particular application. We may consider that a group of persons (a household or a government, for example) is the decision-maker. In doing so, we decide to ignore all internal decisions within the group, and to consider only the decision of the group as a whole. The example described in Figure 1 reflects the decisions of a household, without accounting for all potential negotiations among the parents and the children. We will refer to ``decision-maker'' and individual'' interchangeably throughout the rest of the paper.
Because of its disaggregate nature, the model has to include the
characteristics, or attributes, of the individual. Many attributes, like age,
gender, income, eyes color or social security number may be considered in the
model
.
The analyst has to identify those that are likely to explain the choice of the individual. There is no automatic process to perform this identification. The knowledge of the actual application and the data availability play an important role in this process.