Littering Experiment Challenges Popular Theory on Bystander Intervention

What would you do if you saw a stranger disregarding common rules of conduct in society like talking on a mobile phone during a movie or littering in public? Would you confront them? Call them out to deter them from doing it again? Or just let it slide?

Let’s tweak the question a bit: would your response depend on how serious or negligible the misconduct is?

There’s a popular theory in the field of behavioral social science that if human beings function so well together in modern societies it’s largely because we keep each other in check by handing out some kind of punishment when social norms are ignored. This disciplinary behaviour humans display toward strangers — separate from the laws and penalties imposed by governments and police — is called altruistic punishment. For such punishment to promote cooperative behavior, however, it must “fit the crime." Accordingly, in lab experiments, altruistic punishment has been shown to increase with the seriousness of the offense.

A new study published in Nature Communications, however, has shown the opposite is true in real life, that altruistic punishment from bystanders interested in upholding social order does not always measure up to the “crime".

Fear of retaliation

Field experiments conducted by researchers from NYU Abu Dhabi, University of Innsbruck, and University of Cologne found that most people are unwilling to increase altruistic punishment if the offense is more serious mainly because they fear some kind of retaliation if they speak up.

The research was carried out at two major train stations in Cologne, Germany. Actors violated a social norm by littering in front of unsuspecting subjects. Two variations were played out: one where a violator tossed an empty coffee cup to the ground (a lesser offense) and another where a violator littered a lunch bag full of trash (a greater offense). These variations played out hundreds of times in front of different subjects while researchers watched to see what they would do.


A field experiment tested people's willingness to confront a stranger for littering.

The outcome was unexpected. The study showed that the likelihood of the bystander confronting the violator was exactly the same no matter how big or small the violation.

Study co-author Nikos Nikiforakis, professor of economics at NYU Abu Dhabi, remarked: “The seriousness of the offense increases, but the punishment does not. Since this important condition is not observed in the field, altruistic punishment is unlikely to account for widespread cooperation among strangers in daily life. We probably need another explanation.”

The greater the severity of the violation, the greater was the fear that the violator might be the type of person to retaliate.

Niko Nikiforakis, NYUAD economics professor

Surveys conducted after the field experiment found that most subjects felt more upset with the bigger violation — the discarded lunch bag — and thought it deserved more serious punishment but weren’t willing to do it themselves because they feared it would backfire and the violator would retaliate against them. “The greater the severity of the violation, the greater was the fear that the violator might be the type of person to retaliate,” Nikiforakis explained.

The study and survey results provide “a potential explanation as to why governments and police have emerged to uphold social order,” he added, to handle extreme cases where bystanders are too reluctant to get involved.