Each alternative in the choice set must be characterized by a set of attributes. Similarly to the characterization of the decision-maker described in Section 2.1, the analyst has to identify the attributes of each alternatives that are likely to affect the choice of the individual. In the context of a transportation mode choice, the list of attributes for the mode car could include the travel time, the out-of-pocket cost and the comfort. The list for bus could include the travel time, the out-of-pocket cost, the comfort and the bus frequency. Note that some attributes may be generic to all alternatives, and some may be specific to an alternative (bus frequency is specific to bus). Also, qualitative attributes, like comfort, may be considered.
An attribute is not necessarily a directly observed quantity. It can be any function of available data. For example, instead of considering travel time as an attribute, the logarithm of the travel time may be considered. The out-of-pocket cost may be replaced by the ratio between the out-of-pocket cost and the income of the individual. The definition of attributes as a function of available data depends on the problem. Several definitions must usually be tested to identify the most appropriate.