This supplement contains extended formal results for Daley and Sadowski (2016) (henceforth DS16). Specifically, §S.1 establishes that in Prisoners’ Dilemma (PD) games, the model of DS16 is logically distinct from three models that employ well-known forms of other-regarding preferences: altruism (Ledyard, 1995; Levine, 1998), inequity aversion (Fehr and Schmidt, 1999), and reciprocity (Rabin, 19...