Abstract
Empirical findings on public goods dilemmas indicate an unresolved dilemma: that increasing size—the number of people in the dilemma—sometimes increases, decreases, or does not influence cooperation. We clarify this dilemma by first classifying public goods dilemma properties that specify individual outcomes as individual properties (e.g., Marginal Per Capita Return) and group outcomes as group properties (e.g., public good multiplier), mathematically showing how only one set of properties can remain constant as the dilemma size increases. Underpinning decision-making regarding individual and group properties, we propose that individuals are motivated by both individual and group preferences based on a theory of collective rationality. We use Van Lange's integrated model of social value orientations to operationalize these preferences as an amalgamation of outcomes for self, outcomes for others, and equality of outcomes. Based on this model, we then predict how the public good's benefit and size, combined with controlling individual versus group properties, produce different levels of cooperation in public goods dilemmas. A two (low vs. high benefit) by three (2-person baseline vs. 5-person holding constant individual properties vs. 5-person holding constant group properties) factorial experiment (group n = 99; participant n = 390) confirms our hypotheses. The results indicate that when holding constant group properties, size decreases cooperation. Yet when holding constant individual properties, size increases cooperation when benefit is low and does not affect cooperation when benefit is high. Using agent-based simulations of individual and group preferences vis-à-vis the integrative model, we fit a weighted simulation model to the empirical data. This fitted model is sufficient to reproduce the empirical results, but only when both individual (self-interest) and group (other-interest and equality) preference are included. Our research contributes to understanding how people's motivations and behaviors within public goods dilemmas interact with the properties of the dilemma to lead to collective outcomes.
Highlights
Many human endeavors are neither accomplished nor enjoyed individually, but often people come together and voluntarily cooperate to produce a public good that benefits more than the individual
For the 2 person public goods dilemmas the benefit level was the major predictor of cooperation levels
Consistent with prior work, increased size either promoted more, less, or the same amount of cooperation depending on whether group or individual properties were held constant and benefit level [4, 5, 20]. This interaction between size and benefit dovetails with previous studies that have found at high levels of Marginal Per Capita Return (MPCR) group size no longer has discernible influence on cooperation [31]
Summary
Many human endeavors are neither accomplished nor enjoyed individually, but often people come together and voluntarily cooperate to produce a public good that benefits more than the individual These include a range of large- and small-scale projects such as protecting the environment, electing officials, building libraries, parks, and infrastructure, maintaining charitable organizations, producing collaborative research, keeping a clean house, and competing in a multiplayer game or sport. Individuals often find themselves in a social dilemma with regard to public goods in that they would like to enjoy the benefits of the public good (e.g., a clean environment or a clean house), but contributing to it costs them resources such as time, money, and effort. Public goods dilemmas are a type of social dilemma where all can benefit from a collective resource, a public good, regardless of who contributed to it [2]. Contributing to the public good (cooperating) is never as personally beneficial to one’s own outcomes; not contributing (defecting), while personally yielding more individual benefit, leads to less collective benefit [2, 3]
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