DISCRETE-CHOICE WITH AN ODDBALL ALTERNATIVE

A discrete choice model is presented that explicitly recognizes differ ences in the error structure associated with a single ''oddball'' alte rnative within the choice set that has properties not common to the ot her alternatives. The model purportedly resolves questions related to the use of alternative-specific variables in transportation choice mod els to capture the effects of attributes unique to a single travel alt ernative, such as ''schedule frequency'' in the case of modal choice b etween personal auto and public transit. The model, which shares the g eneral error structure of multinomial legit, is shown to be a modifica tion of a multinomial legit subchoice by terms involving the exponenti al integral. The model is shown to yield different results from those produced by an equivalent multinomial legit specification. Comparisons to multinomial probit and nested legit formulations are also made.