## Social Dilemma and related Definitions

Informally, a *social dilemma* is a collective action
situation in which there is a conflict between individual and
collective interest. It is a situation in which individuals could do
better if they either changed their strategies or changed the rules of
the game.

Some technical definitions:

- Nash equilibrium
- A set of strategies for the players in a game with the property
that no player can benefit by deviating from his or her strategy, and
thereby improve his or her payoffs while the strategies of other
players are unchanged.
- Pareto optimal
- An outcome is Pareto optimal if there is no alternative outcome
that makes some individuals better off and leaves all other
individuals at least as well off.

More formally, a *social dilemma* is a collective action
situation in which the Nash equilibrium results in outcomes below the
Pareto optimal.

A *dominating strategy* is a strategy that yields the best
outcome for an individual regardless of what anyone else does.

Definitions of Nash and Pareto are from Ostrom and Walker (eds.),
*Trust and reciprocity: interdisciplinary lessons from experimental
research*, Russell Sage Foundation, 2003.

Definition of Dominating Strategy from Kollock, P., "Social
Dilemmas: The Anatomy of Cooperation", *Annual Review of
Sociology*, 24: 183-214, 1998.