From Confidence to Spillover Effects: Additions to Support Theory in a Travel-Related Setting

Abstract

Support Theory predicts that breaking down event descriptions into its underlying components (“unpacking”) increases its probability judgment, yielding subadditivity. While robust, its interaction with factors such as personalization—or, more importantly, its implications for later behavior, such as the decision to fly or switch to the train—remains understudied. Study 1 showed that while unpacking significantly increased estimated CO₂ emissions, unlike personalization, it had no direct effect on switching to train. However, an indirect effect of unpacking on switching to train through intention was found. Study 2 replicated the subadditivity effect and identified confidence in one's own judgment of CO₂ emissions as a key variable for predicting intention. Study 3 demonstrates that the results can only be replicated if CO₂ emissions are expressed as a percentage rather than in absolute values (metric tons). Together, these findings extend Support Theory beyond probability judgments and highlight the role of, for example, personalization.