Public Goods Game
A public goods game asks each player whether to contribute to a shared benefit that everyone enjoys whether or not they paid. When contributing costs a player more than it returns to that player, free-riding is the dominant strategy. When the total benefit of contributing exceeds its cost, the two-player version has the structure of a Prisoner's Dilemma.
Payoff matrix
| Row player (rows) / Column player (columns) | Contribute | Free-ride |
|---|---|---|
| Contribute | (4, 4) | (1, 5) |
| Free-ride | (5, 1) | (2, 2) Nash equilibrium |
Payoffs are ordinal scores from the DecisionPlay engine's template for this game, 0 to 5, higher is better. They rank outcomes and are not dollar values. [MODELED]
Nash equilibria
- Pure: Row player plays Free-ride, Column player plays Free-ride. Payoffs (2, 2).
Computed by the DecisionPlay solver from the matrix above. [MODELED]
Where it shows up
Illustrative
- Shared neighborhood upkeep. Each neighbor benefits from a maintained shared space whether or not they helped pay for it, so each is tempted to let the others pay.
- A team project. Every member shares in the finished result, but each would rather spend effort elsewhere and rely on the rest.
Common misreadings
- The model predicts nobody ever contributes. It predicts what incentives alone favor. Real contributions also depend on norms, repeated interaction, and enforcement, which the single matrix leaves out.
- Free-riding means the shared good is worthless. The shared good can be valuable to everyone. The problem is that the individual's cost and benefit from contributing point in different directions.
Try it
Map your own scenario or edit a payoff matrix in the solver.