More generally, to calculate the effect of the switching from cooperation to defection, you have to calculate the reduction in payoff from the public good due to one less cooperator and see whether this is greater or less than $10, the amount an individual defector keeps on top of the public good payoff. You can work this for groups of 1, 2, 3, and 4 cooperators by filling in the following table: Number of cooperators Per capita payoff from public good Per capita payoff when one cooperator switches to defection Change in per capita payoff due to switch Overall change in payoff from switching (for the defector) 1 2 10 8 2 2 4 12 8 2 3 6 14 8 2 4 8 16 8 2