‘tragedy of the commons’ extra credit challenge By Dylan Selterman

Imagine you’re a student and your teacher poses this challenge to the entire class:

You can each earn some extra credit on your term paper. You get to choose whether you want 2 points added to your grade, or 6 points. But there’s a catch: if more than 10% of the class selects 6 points, then no one gets any points. All selections are anonymous, and the course grades are not curved.

I pose this exact challenge to students each semester in my social psychology course at the University of Maryland. This summer, one of my studentshappened to tweet about it, and his reaction went viral. This puzzle has resonated with millions of people around the globe—in the past week I’ve gotten responses from people in Poland, Spain, Italy, Croatia, New Zealand, and Paraguay, to name a few.

This exercise impels students to consider how their actions affect others, and vice versa. I’ve been giving it to students since 2008, and only one class has successfully mastered the challenge. In all other classes, more than 10 percent chose 6 points. Students’ temptation to reach for more points is very strong, and they often express exasperation when things don’t go their way. Last semester after I announced the results, one student threw up her hands and emphatically said, “If only everyone chose 2 points, we all would have gotten the points!”

Many professors in my field use versions of this exercise, which was first developed 25 years ago. I learned it as an undergraduate studying psychology under Steve Drigotas at Johns Hopkins. (I chose 2 points, and watched with extreme frustration as those points were lost when too many of my classmates choose 6 points.) As climate change and population growth threaten our resources, the experiment is more relevant now than ever.

This exercise illustrates the tragedy of the commons (or the “commons dilemma”), and is very similar to other exercises developed by behavioral scientists and game theorists (such as the “prisoner’s dilemma”). In cases like these, there’s a public resource that people can freely use to benefit themselves. In the classroom example it’s points, but in the real world the resource can be food, water, land, electricity, etc. If everyone is mindful about collective consumption and limits their personal use, the group will thrive. But if too many people behave selfishly (trying to maximize their own personal outcomes), then the group eventually suffers and everyone is left with nothing as the public resource is depleted.

It feels good to be cooperative both from a strategic and moral perspective. After all, if every student chose 2 points, everyone would get the extra credit, thus making it a rational choice. Furthermore, it’s the communal choice, based on an ethical imperative to do what’s best for others in the group. But many students choose the seemingly selfish option. Why? Perhaps to increase their own grades, or perhaps because they fear that they will be taken advantage of. No one wants to be the chump that chooses fewer points when they could have had more. The ideal scenario would be if everyone else was cooperative but you were selfish, thereby maximizing your reward while maintaining the health of the group. But it rarely works out that way, and people often find themselves in deadlocks of mistrust with others in their group.


posted by f.sheikh