Data from: Group size effect on cooperation in one-shot social dilemmas II: curvilinear effect

In a world in which many pressing global issues require large scale
cooperation, understanding the group size effect on cooperative behavior
is a topic of central importance. Yet, the nature of this effect remains
largely unknown, with lab experiments insisting that it is either positive
or negative or null, and field experiments suggesting that it is instead
curvilinear. Here we shed light on this apparent contradiction by
considering a novel class of public goods games inspired to the realistic
scenario in which the natural output limits of the public good imply that
the benefit of cooperation increases fast for early contributions and then
decelerates. We report on a large lab experiment providing evidence that,
in this case, group size has a curvilinear effect on cooperation,
according to which intermediate-size groups cooperate more than smaller
groups and more than larger groups. In doing so, our findings help fill
the gap between lab experiments and field experiments and suggest concrete
ways to promote large scale cooperation among people.