Similarity and decision time in preferential choice.

Choice option similarity is a key contextual variable in multiattribute choice. Based on theories of preference accumulation, we predicted that decision times would be longer when the available choice options were similar compared with when they were dissimilar, controlling for the relative desirabilities of the options. We tested for the relationship between similarity and decision time in an experiment involving incentivised binary choices between items of equivalent desirability and found that our predictions were confirmed. Our results show how the effects of contextual factors on key decision variables can be accurately predicted by existing computational theories of decision-making.