Similarity and Moral Trade-offs

Alex Voorhoeve, Arnaldur S. Stefansson, and Brian Wallace


How, and how reliably, do people make difficult moral trade-offs? We pursue this question through an experiment in which subjects must choose to save either a larger number of people from smaller harm, or, instead, a smaller number of people from greater harm. Our results indicate that around 40% of subjects use a similarity heuristic to make such choices. When alternatives appear dissimilar in terms of the number of people one can save from harm but similar in terms of the severity of harm from which they can be saved, this heuristic mandates saving the greater number. In our experiment, use of this heuristic leads to violations of principles of rational choice at the individual and collective level. It also leads to individual and collective choices that are inconsistent with all standard theories of distributive justice. We argue that this demonstrates the unreliability of moral judgments in cases that elicit similarity-based choice.


Appendix 1: Instructions and all questions

Appendix 2: Further statistical analysis

Appendix 3: Excel sheet of subjects' choice data and rationales