Issues in the specification of regret-only choice models : a rejoinder to Chorus and Van Cranenburgh

Before starting the debate, we would like to state explicitly that we share Chorus and Cranenburgh’s (C&C) concerns about prevailing confusion about regret-based models and their fascination of exploring the value of context-dependent choice models in transportation research and beyond. Although the number of applications of random regret models has gradually increased over the last decade, still there are many non-believers as evidenced by critical, skeptical questions at conferences, questionable paper reviews and the contents of informal discussions. First, some peers have questioned their theoretical foundation, as they are not based on classic axiomatic theorems of rational decision-making. Second, the relevance of random regret models has been downplayed as empirical studies have shown that even if these models perform better than random utility models, their performance is only marginally better. Therefore, it has been argued their further development is not very worthwhile. Thirdly, compromise effects may have been observed in some marketing studies, doubts have been raised about their importance in transportation. Finally, we have often heard that because choice probabilities in both the MNL and random regret models are based on utility/regret differences, the models are fundamentally the same; although most MNL models assume a linear-additive utility function, there is no reason not to use non-linear (reference-based) functions, fading out their difference. These skeptics argue we do not need the concept of regret; the concept of utility is sufficient to formulate more flexible choice models. These reactions suggest a lot of confusion and lack of understanding of regret models. We have no desire to further contribute to this situation and therefore like to take this opportunity to further explain the considerations that led to our 2016 paper (Rasouli and Timmermans 2016) and articulate our opinions in response to C&C’s comments.