Impact of choice set complexity on decoy effects

Studies of contextual choice typically use three option choice sets to evaluate how preference relations depend on the values of a third decoy option. However, often real-world decisions are made using choice sets with many more than three alternatives, such as in online shopping. Three experiments tested for attraction and compromise decoy effects in choice sets that varied the number and ordering of alternatives using a within-subjects preferential choice grocery shopping task. In Experiment 1, attraction and compromise effects were significantly reduced as alternatives increased from three to nine. Experiment 2 found significantly greater attraction effects in nine alternative choice sets ordered by attributes compared with a random ordering. Experiment 3 used eye tracking and found significant attraction effects in choice sets with 3, 9, and 15 alternatives, but the effect was reduced with increasing alternatives. Eye tracking revealed that participants engaged in more by-dimension comparisons as the number of alternatives increased, but, contrary to previous research, the proportion of by-alternative to by-dimension transitions was not linearly predictive of decoy effects. With increased alternatives, the proportion of the total information attended to decreased, leading to worse choice outcomes, and participants were more likely to engage in a lexicographic decision-making strategy.