We conducted three studies including one lab and two online experiments. The studies were approved by the local ethics committee of Göttingen University’s Psychological Department and conducted in accordance with the approved guidelines. Before conducting the studies, we obtained informed consent from all subjects. With the methods and instructions used, we strictly replicated the previous core investigation by Rand and colleagues4, except for some important extensions. Participants played one-shot public good games (PGG) in groups of four. In the PGG, independent and anonymous individual contributions of each member were doubled and split evenly among the members of the group.

The basic procedure is described in Fig. 1. After group assignment, participants were presented with an instruction screen describing the structure and the rules of the game. After reading the screen, participants clicked a continue button to proceed to the response screen, which contained the request to indicate the amount of money (in cents) they wish to contribute. Participants indicated their contributions by typing a number in the respective field and confirmed their input with a mouse click on a continue button. The time between onset of the response screen and the confirmation of the contribution by mouse click constituted our main predictor variable decision time. Hence, decision time exclusively captures the time required for generating the response concerning how much to contribute. The reading time of the Public Goods Game instructions was explicitly detached by displaying instruction on a separate screen.

Figure 1: Procedure of the studies. Note: PGG refers to Public Goods Game, SVO stands for Social Value Orientation. Full size image

Decision time was measured via the programs used for data collection (i.e.‘Unipark’ for the online studies and ‘Bonn Experiment System’ for the lab study). In the first study we analyzed data of 134 Amazon Mechanical Turk (MTurk) workers (51 female, mean age = 30.5 years) half of them from the United States and the remaining from other western countries and India. Second, we elaborated these results in a more controlled setting and conducted a laboratory study with mostly German students (N = 105, 70 female, mean age = 26.97 years). Finally, as a third experiment, we conducted a high-power online study with representative samples concerning age and gender for the US (N = 249) and German populations (N = 255), resulting in a total sample of N = 504 (258 female, mean age = 46.13 years). Data for the third experiment was gathered via a professional panel provider. The endowment for the PGG varied between studies (i.e., USD 0.40 in the first study conducted on MTurk, 2.00€ (approx. USD 2.70) in the lab experiment and USD 1.50 in the third study (Panel)) but the multiplication factor of two for contributed money remained constant.

In line with previous studies we additionally gathered data about beliefs (the expectations about the other players’ cooperation behavior) as well as cooperativeness of interaction partners in daily life and previous experience with the experimental setting of social dilemma games. As an important extension, we additionally measured social value orientation using the SVO Slider Measure16 at the end of the study, which allows to calculate a continuous SVO angle value. An angle of around zero indicates proself persons; these are persons that maximize their own outcomes without considering outcomes of others. Positive values indicate more prosocial behavior in that people gain positive utility from outcomes of others. The SVO measure was incentivized and it was common knowledge that it was determined by a random draw whether the PGG or the SVO were incentivized. In order to check for correlations with broader personality factors, we included the 60 items general personality questionnaire HEXACO at the end of the third study17. More details on the procedure and the fully instruction are provided in the supplementary online materials.