Accounting for Preference and Scale Heterogeneity in Establishing Whether it Matters Who is Interviewed to Reveal Household Automobile Purchase Preferences

The choice of automobile purchases in households often involves participation of more than one household member, each of which exerts some degree of influence on the final choice outcome. The influence of more than one agent has been recognised for many years, and yet the majority of automobile choice studies develop choice models as if a single agent is involved in the preference revelation process. What is not clear is whether it makes any substantive difference in preference revelation according to who is interviewed in a household. Using a generalised mixed logit framework that accounts for preference and scale heterogeneity, we estimate a series of models to investigate whether there are significant differences between the preferences of each individual in a household when assessed in isolation from other household members, as well as their joint preferences when expressing their preferences through a group choice task. The context is choosing amongst petrol, diesel and hybrid fuelled vehicles (associated with specific levels of fuel efficiency and engine capacity) when faced with a mix of vehicle prices, fuel prices, fixed annual registration fees, annual emission surcharges and vehicle kilometre emission surcharges. Using a stated choice experiment, we find that sampling a single individual as a representative of the household’s preferences is less appropriate than utilising preference information from the relevant group of decision makers in the household.