A group benefits if one person volunteers to pay a small cost. Does a bigger group help?
Imagine a group where everyone benefits if at least one member volunteers for a small, costly task — calling for help, reporting a gas leak, anything unpleasant but necessary. Everyone would rather someone else do it. As the group gets bigger, does each individual become more likely to step up, less likely, or does it stay the same?
Reveal the answer
Less likely. In the game's unique symmetric equilibrium, each person's probability of volunteering actually falls as the group grows, and the odds that absolutely nobody volunteers rise with group size — the mathematical backbone of the real-world bystander effect. Sociologist Andreas Diekmann formalized the game in 1985.
— Andreas Diekmann, Volunteer's Dilemma — Journal of Conflict Resolution, 1985