85 Do nice guys finish first or last? Refer to the Nature (March 20, 2008) study of the use of punishment in cooperation games, Exercise 18 . Recall that college students repeatedly played a version of the game “prisoner’s dilemma” and the researchers recorded the average payoff ( y ) and the number of times punishment was used ( x ) for each player.

A negative correlation was discovered between x and y .

a. Give the null and alternative hypothesis for testing whether average payoff and punishment use are negatively correlated.

b. The test, part a , yielded a p -value of .001. Interpret this result.

c. Does the result, part b , imply that increasing punishment causes your payoff to decrease? Explain.