Fig. 1.

The lottery choice paradigm and repeated happiness measurements. In the initial laboratory session, each participant chose between two lotteries, the “prosocial” Lottery A and the “selfish” Lottery B. Based on their individual lottery draw, subjects either received 100 euros or saved one human life in expectation, in which case the experimenter transferred a donation of 350 euros to a charity that fights tuberculosis. The laboratory session was followed by an online survey 4 wk later. We elicited happiness three times: at the beginning ($H_{\mathrm{B}\mathrm{a}\mathrm{s}\mathrm{e}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}}$) and at the end ($H_{\mathrm{S}\mathrm{h}\mathrm{o}\mathrm{r}\mathrm{t}-\mathrm{r}\mathrm{u}\mathrm{n}}$) of the laboratory session and again in the survey ($H_{\mathrm{L}\mathrm{o}\mathrm{n}\mathrm{g}-\mathrm{r}\mathrm{u}\mathrm{n}}$). We sent out two personalized emails reminding participants of their individual lottery outcome between the laboratory session and the survey.