Cooperation is an essential aspect of life, from bacterial biofilms to social insects, and from friendships and workplace collaborations to environmental conservation, political participation, and international relations. Yet establishing cooperation in a competitive world suffers from two closely connected problems. For one, there is the risk for cooperators to be the “sucker”, i.e. one of the few people cooperating while everyone else freerides on their efforts.  But we also face the temptation to follow our self-interest and to freeride on others ourselves.

My research shows that in many situations it is not so much temptation, but instead the risk of being the “sucker” that prevents people from cooperating. Hence it is not because we are greedy or because human nature is evil that we often fail to cooperate. Instead, most of the time, it is our worry about being exploited by others that keeps us from cooperating.

To study cooperation under controlled conditions, I use “economic games”, where participants are given money and choose how much (if any) to spend on benefiting others. One such game is the prisoner’s dilemma game.  In the prisoner’s dilemma game two people choose between two actions: cooperate or defect. Crucially each of them has to choose without knowing what the other is choosing. If both cooperate they both get a good payoff, if both defect their payoff is lower.

So far things seem easy – it is better for both to cooperate. The dilemma lies in the fact that each is best off if they defect while the other person cooperates (temptation) and they are worst off if they cooperate while the other person defects (risk). Because of the simplicity of the game and how it captures the trade-off between self-interest and collective interest, the prisoner’s dilemma has been studied for over 50 years in areas as diverse as biology, economics, political science, physics, psychology or sociology as a workhorse to understand civic behaviour or why people cooperate in social dilemma situations. For our research I collected data from 96 different prisoner’s dilemma games played with more than 3500 people across six different countries.

I find that cooperation rates are high whenever the game presents low risk. This is particularly the case in so-called one-shot games in which participants interact only once and don’t have the possibility to establish a reputation. By contrast, the extent of temptation does not seem to be too important in these games. These effects are persistent and do not become weaker after participants have gained experience in these interactions.

Do risk and temptation affect both women and men equally? The answer is “No”. If risk is low then women tend to be more cooperative than the average man and if it is high they tend to be less cooperative. This also means that there is no universal answer on whether women or men are more cooperative. It depends on the underlying risk.

You might be familiar with a prisoner’s dilemma type situation if you have ever watched the game show “Golden Balls: Split or Steal?” . The two final contestants in this show independently have to decide whether they want to “split” or “steal” the jackpot. If both contestants choose split, they share the jackpot equally. If one chooses split and the other chooses steal, the one who steals takes the jackpot and the other gets nothing. If they both steal, both go home empty-handed. The risk is small in this show as splitting or stealing makes no differences to my outcome if the other person steals. (I get nothing in this case no matter what I do). The temptation to steal the entire jackpot, by contrast, is substantial. Data from this show were studied by a team led by Martijn van Assem in 2012, who found that cooperation is “surprisingly high” in this game, in line with the low risk the game presents.

In fact, social dilemma situations that involve a tension between self and group interest are at the heart of many interactions, not only game shows, but also effort provision in teams, tax compliance, public good provision or simply good citizenship behaviour. This research hence has potential implications for the design of policies. If policy makers can reduce the risk associated with cooperating, e.g. via information campaigns or direct transfers, then this is likely to be more promising than attempts to reduce temptation.



Friederike Mengel is a professor of economics at the University of Essex and a visiting guest professor at Lund University. She is also a co-editor of the Journal of Economic Behavior and Organization, an associate editor at the Economic Journal and the European Economic Review and a member of the editorial board of Experimental Economics and the Journal of Behavioral and Experimental Economics. She got her PhD in 2008 from the University of Alicante.