Why 'carrots trump sticks,' or, why 'winners don't punish'

Does punishment or reward work better at influencing human behavior? It's a question that's seemingly fundamental to what goes on in the justice system, but one that's seldom subjected to empirical analysis. So I found this discussion of public-goods games by Ed Yong at Not Exactly Rocket Science a fascinating train of thought. He writes that:

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, [David] 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.

According to Rand's research:

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 where 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.

These results strike me as having implications at a societal level for the criminal justice system. Punishment can be an effective way to foster cooperation with social norms, according to these results, but over time the cost of retaliation is excessive. Perhaps this finding may be analogized to the rise of mass incarceration in the United States over the last three decades? Even to the extent it's been effective at enforcing social norms, at this point society has reached a stage where we can no longer afford to use this tactic exclusively, or so this blog has repeatedly argued.

Yong questions whether Rand's analysis applies in a globalized world, but it seems to me that when considering incarceration as punishment, the model works as well in macro as in micro - at least in regard to punishment's negative impacts. The vast majority of offenders who go to prison later get out, so society cannot have a one-and-done attitude toward them without facing negative consequences.

Similarly, emphasizing punishment over reward reduces overall wealth, according to this theory, just as it's the case that prisons both cost society a lot to run and incur significant opportunity costs from the lost wages and productivity of the incarcerated. In the real world as in game theory, the benefit to public order derived from punishment comes at a severe and mounting economic price that reduces wealth for everyone.

For more on this research, see a related article from Nature published last year, "Winners Don't Punish" (pdf).