Why we should clean up litter and graffiti

Broken windows theory asserts that norm-violations are often self-perpetuating. In a neighbourhood that is pervaded by signs of norm-violation (e.g., litter, graffiti, broken windows), people will be more likely to violate social norms themselves. The reason being that the presence of such signs leads people to conclude that wanton norm-violations evidently go unpunished in that neighboured. An important implication of broken windows theory is that the costs of public bads such as litter are greater than those entailed by their mere unsightliness. 

There is both correlational and experimental evidence for broken windows theory. Consistent with earlier studies, Schultz et al. (2011, Environment and Behavior) found that the amount of litter present at a site was positively associated with the littering rate. Similarly, Nettle et al. (2011, PLOS ONE) documented that individuals were less likely to return a letter in a neighbourhood where there was more litter. Keizer et al. (2008, Science) famously showed, using field experiments, that individuals were more likely to drop litter in a passageway when it was covered in graffiti, and that they were more likely to steal €5 from a postbox when it was surrounded by litter. Some of their results were questioned on methodological and statistical grounds by Wicherts & Bakker (2014, Group Processes & Intergroup Relations). Yet two further studies (Keizer et al., 2013, PLOS ONE; Keuschnigg & Wolbring, 2015; Rationality and Society) have bolstered the conclusion that people are more likely to violate social norms where signs of norm-violation prevail.

Since many policy makers are probably not aware of these results, they may well be under-allocating resources to the prevention and removal of litter, graffiti and broken windows etc. One prescription would be to increase the penalties for littering (and other such things) in order to deter prospective norm-violators. Another (more contentious) prescription would be to fine landlords, home-owners and businesses who permitted litter and graffiti to accumulate on or around their properties. While not especially fair, this policy would give property-owners themselves an incentive to take precautions against norm-violators. Indeed, they might be in a better position to take such precautions than policy-makers would be to impose them. The trick would be setting the fine appropriately.