Carrots Trump Sticks for Fostering Cooperation

From:

Not Exactly Rocket Science

Posted by Ed Yong on September 3, 2009

When it comes to encouraging people to work together for the greater good, carrots work better than sticks. That’s the message from a new study showing that rewarding people for good behaviour is better at promoting cooperation than punishing them for offences.
David Rand from Harvard University asked teams of volunteers to play “public goods games”, where they could cheat or cooperate with each other for real money. After many rounds of play, the players were more likely to work together if they could reward each other for good behaviour or punish each other for offences. But of these two strategies, the carrot was better for the group than the stick, earning them far greater rewards. .
Public goods games, albeit in a more complex form, are part and parcel of modern life. We play them when we decide to take personal responsibility for reducing carbon emissions, or rely on others to do so. We play them when we choose to do our share of the household chores, or when we rely on our housemates or partners to sort it out.

These sorts of games are useful for understanding our tendency to help unrelated strangers even if we stand to gain nothing in return. The big question is why such selflessness exists when altruists can be easily exploited by cheats and slackers, who reap common benefits without contributing anything of their own. How does selflessness persist in the face of such vulnerabilities?


Many researchers have turned to punishment for an answer, testing the idea that societies are glued together by the ability to mete out penalties to freeloaders, often at some personal cost. Long -time readers of this blog may remember a set of articles on this topic.

The first, from Simon Gachter’s group, showed that the ability to punish freeloaders stabilises cooperative behaviour, but a second study from Martin Nowak showed that this boost in cooperation carries a cost – by escalating conflicts, the ability to punish leaves groups with smaller rewards than those that shun punishments altogether. Gachter disagreed, and in a third study, his group suggested that in the long run, both groups and individuals are better off if punishment is an option. Now, Rand, part of Nowak’s group at Harvard University, is back with another take on the debate and this time, he has focused on punishment’s cuddlier counterpart – reward.

This time, Rand wanted to make the games more realistic. Often, they are played for single rounds or with constantly switching anonymous partners. But that’s hardly an accurate reflection of real life where, as Rand says, “repetition is often possible, and reputation is usually at stake”. We often interact with the same people again, and our attitudes toward them depends on our past dealings. So Rand wanted to tweak the public goods game so that reputation could play a role.

Rand recruited 192 volunteers who played the game anonymously over computer screens. They were split into groups of four who stayed together throughout the experiment. The games lasted for 50 rounds, although the players didn’t know this. In each round, the players decide how many of 20 units to contribute to a public pool and how many to keep for themselves. The common pot is multiplied by 1.6 and divided evenly. At the end of it all, the units were converted into real cash.

It’s a classic dilemma. The group does best if everyone puts in their full allocation and all the players get 32 units back. But for a single player, the best tactic is to hold everything back and reap a share of the other players’ contributions – by doing so, they could end up with a princely 44 units.

On top of this basic model, some of the recruits played games with a second stage to each round. During this stage, one group could punish a specific player, paying 4 of their own units to deprive the victim of 12 of theirs. A second group could reward their peers with 12 units at the cost of 4 of their own. And a third group could choose between rewards, punishment or inaction. At the end of it, each player learns what their peers did to them, but not to the others.
With neither carrots nor sticks on the cards, Rand found that the players’ average contributions fell over time from 14 units per round to a mere 8. However, both rewards and punishment were equally good at promoting cooperation; when these options for interaction were available, the contributions stayed high. However, the two groups that could reward each other earned much higher payoffs than those that could only punish, or those that could do neither.

People also seemed to like playing the do-gooder; in both groups were rewards were available, players used them more and more as the games went on. Punishments, however, decayed over time. The cost of retaliations meant that players hardly ever doled out penalties by the experiment’s end. In fact, when both options were on hand, the groups that largely rewarded each other ended up wealthier than those that favoured punishments.

A few questions remain. Rand’s modified public goods game was designed to allow reputation to influence how people hand out reward and punishment. This reflects many of our most important interactions – with friends, family and colleagues – and it certainly reflects the world of our ancestors, who lived in tightly knit communities. Whether it applies to our globalised world, where we may only have one-off encounters with others and where online communication offers the boon of anonymity, remains to be seen.

But all in all, Rand’s results suggest that when people repeatedly cross each other’s paths, carrots are far better than sticks at fostering behaviour for the greater good. Not only do they lead to greater payoffs for everyone concerned but they minimise the threat of antisocial punishment, where freeloaders vengefully castigate the altruists. This behaviour has the ability to derail cooperation and while fairly rare in countries like the US or the UK, it is far more common in places like Greece and Oman. In such countries, the relative merits of rewards may be even greater.

Rand sums it up best in his own conclusions and I will let his words speak for themselves:

“Sometimes it is argued that it is easier to punish people than to reward them. We think this is not the case. Life is full of opportunities for mutually beneficial trade, as well as situations where we can help others, be they friends, neighbors, office mates, or strangers. We regularly spend time and effort, as well as money, to assist people around us. This assistance can be minor, like helping a friend to move furniture, working extra shifts to cover for an ill co-worker, or giving directions to a tourist. It can also be more important, like recommending a colleague for promotion or speaking out to support a victim of discrimination. These sorts of productive interactions are the building blocks of our society and should not be disregarded.”