Graffiti Matters

Graffiti Matters

Graffiti has unintended side effects.


Cleaning up the streets. I'm Bob Hirshon and this is Science Update.

Would you break the law just because someone else did, too? It turns out that many people will. Social scientist Kees Keizer of the University of Groningen in the Netherlands ran experiments on unsuspecting people. His team discovered that people were almost twice as likely to litter in an alley that was full of graffiti compared to a clean one. And they were also about twice as likely to steal an envelope full of money from a mailbox if there was graffiti on the box.


To our amazement, I must say. We expected an effect, but there were people I least expected to take the envelope.

Keizer says this shows that when rule-breaking behavior becomes common, it leads to more and different rule-breaking behavior. That’s something to consider the next time you’re tempted to litter. I’m Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

We'd all like to think that we behave according to our moral and ethical standards, no matter what the situation. But this experiment illustrates the fact that our behavior depends a lot on our immediate surroundings.

The experiment itself was fairly simple and self-explanatory. Its implications would seem to support a popular approach to crime prevention called the “Broken Windows Theory,” which gets its name from a 1982 article by sociologist George Kelling and political scientist James Q. Wilson. At the time, crime rates were rising all across America, especially in cities. Kelling and Wilson argued that small crimes lead to bigger crimes, and visible signs of neglect, like broken windows, graffiti, and litter, create conditions that make people more likely to commit crimes. They give an example very much like the situation Keizer's team created: “Consider a sidewalk. Some litter accumulates. Soon, more litter accumulates. Eventually, people even start leaving bags of trash from take-out restaurants there or breaking into cars.”

Kelling went on to consult with New York City's transit and police departments, and his theories were implemented on a number of levels. Transit workers scrubbed graffiti off subway cars and arrested fare-jumpers. Police began cracking down on petty nuisance crimes like loitering, public urination, and public drunkenness—crimes that were once considered too minor to bother prosecuting. Indeed, major crime in New York City soon plummeted, from an all-time high in 1990 to record lows in the late 2000s.

Now, many factors may have contributed to this decline in crime, including more police on the streets, improved crime-fighting technology, a booming economy, low unemployment, and the fading of the crack epidemic that fueled many murders, robberies, and assaults in the 1980s. It's difficult, if not impossible, to say for sure if the Broken Windows Theory had a real impact, and if so, how much it contributed. (Some critics note that during the same time period, crime declined in other cities where “broken window” measures were not implemented.) The enforcement of the Broken Windows Theory also has been controversial: some have argued that it encouraged harassment and brutality by police, or unfairly targeted certain groups.

However, Keizer's experiment certainly suggests that our environment can affect our behavior, and even ethical people may break the law under certain conditions. In fact, humans have proven themselves to be easily influenced in other, more chilling ways. One of the most famous experiments of the 20th century was conducted by Yale University psychologist Stanley Milgram in 1961. Milgram found that a majority of people he studied were willing to administer what they believed to be increasingly painful electric shocks to another person, simply because the rules of the experiment required it. (In reality, there was no shock: the person receiving it was an actor, pretending to be in pain.) Many kept going even when the actor banged on the wall, complained of his heart condition, and eventually stopped moving.

Another landmark study, the “Stanford prison experiment,” was conducted by researchers at Stanford University in 1971. Twenty-four college students, all with no history of psychological or social problems, volunteered to spend two weeks in a fake prison created in the basement of Stanford's psychology building. Half of the volunteers were assigned to be “guards,” the other half were assigned to be “prisoners.” The guards received uniforms, and the prisoners wore ankle chains and rags. By the second day, the guards began cruelly harassing the “inmates.” The inmates rioted against the guards, who sprayed them with fire extinguishers (without the knowledge of the experimenters). Prisoners seemed to take their captivity so seriously that they didn't walk away from the situation—even though they were legally free to do so—and accepted defeat when their applications for “parole” were denied. The researchers abandoned the experiment after only six days, in order to prevent further psychological damage.

If people can be made to inflict serious physical or psychological pain on others, simply by creating an environment that permits it, it's not so hard to believe that we might also litter or even steal if our surroundings seem to encourage such behavior. It also suggests that simply dropping a gum wrapper on the sidewalk could set off a domino effect that leads to surprisingly serious consequences.

Now try and answer these questions:

  1. What was the result of Keizer's study?
  2. What is the Broken Windows Theory? How does it relate to this study?
  3. Have you ever behaved differently—either better or worse—because of the environment you were in? What elements of the environment do you believe influenced your behavior?
  4. What do this experiment, Milgram's experiment, and the Stanford prison experiment say about human nature?
  5. Both Milgram's experiment and the Stanford prison experiment influenced later policy on the ethics of using humans in psychological studies. From a scientific standpoint, what ethical issues do these experiments raise? 

You may want to check out the December 26, 2008 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: cleanliness clouds moral judgment, the genetics of the placebo effect, secrets of master impressionists, and more.

Going Further

For Educators

One of the original researchers, Philip G. Zimbardo, maintains a website devoted to the history and implications of the Stanford Prison Experiment.

The New York Times article Four Decades After Milgram, We’re Still Willing to Inflict Pain describes a 2008 replication of the Milgram experiment, with similar results.

Malcom Gladwell's books, The Tipping Point: How Little Things Can Make a Big Difference (ISBN 0-316-31696-2) and Blink: The Power of Thinking Without Thinking (ISBN 0-316-01066-9), include provocative discussions of the Broken Windows Theory, the Stanford and Milgram experiments, and the power of context in influencing human behavior.

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