Framing car fuel efficiency: linearity heuristic for fuel consumption and fuel-efficiency ratings

People are sensitive to the way information on fuel efficiency is conveyed. When the fuel efficiency of cars is framed in terms of fuel per distance (FPD; e.g. l/100 km), instead of distance per units of fuel (DPF; e.g. km/l), people have a more accurate perception of potential fuel savings. People tend to treat both DPF and FPD as linearly related to fuel consumption, while the relationship between DPF and fuel consumption is in fact curvilinear. We examined whether these incorrect assessments would also affect hypothetical car purchase choices in situations where cars also differ in relevant aspects other than fuel efficiency. Three experimental studies suggest that participants consistently employed a linearity heuristic, resulting in less optimal car choices in a DPF than in a FPD frame, and that this linearity heuristic for fuel efficiency with fuel consumption persists in the face of variations of important characteristics unrelated to fuel efficiency.