The "Broken Windows Theory" is based on the idea that urban disorder such as broken windows and graffiti(落書き)encourages petty(軽微な)crime. In a series of experiments investigating whether people would be more willing to violate social rules if they saw evidence that others already had, researchers found that people were more likely to litter(ごみを散らかす), trespass, and even steal when they saw evidence of others ignoring the rules of good behavior. In one experiment, passersby were observed to be twice as likely to steal an envelope full of money when the mailbox had been defaced(外観を損なう)with graffiti or when the surrounding area had litter lying around.