On Confounding Preference Heterogeneity and Income Effect in Discrete Choice Models

A substantial part of the discrete choice model literature has been concerned with specifications accounting for preference heterogeneity. In contrast, only a few studies have been interested in the presence of income effect, and it is much rarer still to come across models trying to account for both effects simultaneously. In this paper we use a specification that accounts for income effect and preference heterogeneity, both of a systematic and of a random nature. Our results point out that care should be taken with conclusions drawn from studies that only consider these effects separately, since they can be confounding from an empirical point of view. In fact, we provide empirical evidence that a random cost parameter can account for the existence of income effect.