Each red card the student keeps generates four dollars in personal earnings. Students also earn one dollar for each red card that is played by the entire class. Thus, playing a red card is equivalent to contributing to the provision of a public good. After the instructor collects two cards from each student, the number of red cards is tallied and student earnings determined. The cards are returned to the students and a new decision round begins.
Large classes can simply use a subset of students.
You will need one deck of playing cards for every 13 students. Reduce the value of the kept red cards to two dollars after several decision rounds. Communication among students may be allowed in order to facilitate group decision making. Instructors may also want to vary the size of the group or allow students to revise contributions. Each group is then informed that the current pollution level in their area exceeds national standards and must be reduced.