Revisiting External Validity: Concerns about Trolley Problems and Other Sacrificial Dilemmas in Moral Psychology

Trolley problems are becoming the most recognizable rhetorical examples of moral judgment. They have helped attract popular and scholarly attention to morality, especially over the past decade. However, philosophical thought experiments are not designed to meet the methodological standards of experimental psychology, and using trolley problems as experimental stimuli threatens the validity of the science. Supporting this claim, four empirical studies highlight two methodological problems associated with using trolley problems in psychological research: (1) variants of the trolley problem usually differ in several ways, which limits the internal validity of studies that compare responses across variants, and (2) trolley problems often lack psychological realism, which limits the external validity of trolley studies. In sum, philosophers and psychologists approach questions of morality from different viewpoints, which necessitate different methods. Prior research that has used trolley problems has been generative, but the field has reached a point where it should do better.