Self-fulfilling prophecy: People's opinion of others determines how cooperative they are

In previous studies, other researchers had successfully put participants in Bonn and London into a social dilemma with such games, which are very popular in experimental economics. Engel, Kube and Kurschilgen used them as a template for their study, which focuses on an aspect that ought to be of interest to social policymakers and town planners too. "We wanted to find out whether the 'broken windows' theory held true in the lab as well," explained Michael Kurschilgen.

According to this theory, minor details, like broken windows in abandoned buildings or rubbish on the streets, can give rise to desolate conditions like the utter neglect of a district. "Such signs of neglect give people the impression that social standards do not apply there," says Kurschilgen, explaining the idea behind the theory, which was the motivation behind New York mayor Rudy Giuliani's decision to embark on the zero-tolerance strategy he employed to clean up the city in the 1990s.

In their study, the three MPI scientists tested the theory in a scientific experiment. Using the kind of public good games that are often applied in the field of experimental economics, their aim was to find out the extent to which first impressions determine how people will behave, and the extent to which this can be influenced by selective information. The games are set up around the classic dilemma of self-interest and socially minded behaviour: each member of a group of four players is given the sum of 20 tokens. They can either keep these for themselves or invest them in a community project. Each player receives 0.4 tokens in return for each tokens they invest in the community project. If all four group members invest their 20 tokens, each one of them receives 32 tokens, in other words 12 tokens more than if they all keep the money for themselves. But if only three of them invest their money in the community, the selfish fourth player gets 44 tokens.

So even the free rider profits from the other players' investment in the community fund. "The public good game thus creates a social dilemma," explains the economist. That's because it would be best for the community if everybody invested in the collective. However, on an individual level the free rider gets the best out of it. They ultimately receive the bonus without having made the investment.

Surprisingly, there are significant differences between Bonn and London in the willingness to invest in the common good. Londoners invested a mere 43 per cent, on average, in the common good. In Bonn, on the other hand, the figure was 82 per cent. "This is probably down to differing expectations of what constitutes normal behaviour," postulates Kurschilgen. Individuals who assume that the others will act selfishly too are hardly likely to commit altruistic deeds themselves. "From that point of view, Londoners have a more pessimistic view of man than do the participants in Bonn," he concludes in respect of the Brits' reticence. Consequently, whether a person decides to behave cooperatively or not depends strongly on how that person thinks the other players will behave.

In their series of experiments, Engel, Kube and Kurschilgen told their newly recruited players from Bonn the results of the London study. The players in the new round of games evidently reacted very negatively to the information that few of the players in the previous experiments in London had exhibited cooperative behaviour. Unlike the virtuous people of Bonn from the previous rounds, they showed far fewer pretensions of being good citizens: instead of investing more than 80 per cent in the common good, the participants in these experiments contributed just 51 per cent, on average. Therefore, the negative information was enough to revise the previously positive image held by the Bonn residents. This model did not really work the other way around -- good examples did not make bad teammates into goody two-shoes.

"Our findings demonstrate that the core of the 'broken windows' theory does actually hold true. Faced with a social dilemma, people are guided to a very great extent by their original expectations of what other people will do, but they are also particularly sensitive to negative impressions," says Kurschilgen, summing up the observations. Given this conclusion, it is clear to him that every cent spent on maintaining residential districts does more than just make the neighbourhood look prettier -- it also represents a sound investment against crime.