Discrete choice with an oddball alternative

A discrete choice model is presented that explicitly recognizes differences in the error structure associated with a single ‘oddball’ alternative within the choice set that has properties not common to the other alternatives. The model purportedly resolves questions related to the use of alternative-specific variables in transportation choice models to capture the effects of attributes unique to a single travel alternative, such as ‘schedule frequency’ in the case of modal choice between personal auto and public transit. The model, which shares the general error structure of multinomial logit, is shown to be a modification of a multinomial logit subchoice by terms involving the exponential integral. The model is shown to yield different results from those produced by an equivalent multinomial logit specification. Comparisons to multinomial probit and nested logit formulations are also made.