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Cornell’s Broken Windows

Consider an urban neighborhood where there are numerous broken windows. Theory states that the probability of additional crimes increase significantly due to the perception of a lack of monitoring of the location. In other words, if a potential criminal believes there is a greater chance of success in illegal acts she is more likely to partake in the crime. Likewise a neighborhood that is well maintained then there is less of a chance of illegal activities such as vandalism to take place. This idea can be extended to a larger neighborhood: the zip code of 14853 that we love to call Cornell.

As many students can testify, recently there have been a large outcry to protect student against the dangers of sexual offenders in the night. Each weekend students are reminded to travel in groups, males are encouraged to walk females home to ensure their safety. The university is taking measures to prevent these incidents at large. However a question that must be asked is how effective is the strategy suggested and encouraged by the university.

One argument is that by informing students of the dangers of the night they are exposing the “broken windows” on campus for all to see. By seeing the additional crimes on campus these potential sexual offenders may feel encouraged to act on the thoughts they have. Students may feel the need to commit other crimes because they know they can get away with the deed. However another argument stands. By openly exposing the open windows one may say Cornell is placing security on the windows to discourage others from “breaking more windows”.

Let’s examine this effect with Bayes’ Law. We want to determine the probability that sexual offenses will occur given that students know the extent of offenses that already occur on campus, P(A|B). On a crude level this should be equal to the probability that students know the extent of offenses that already occur on campus given sexual offenses that occur, P(B|A),  times the probability sexual offenses occur, P(A),  divided by the probability students are aware of the of the sexual offense situations on campus, P(B).

Due to Cornell’s efforts P(B) has increased compared to before this semester. However P(B|A) also increases for the same reasons. However I argue this does not increase as much as P(B) because students are not aware of the full extent of what happens in the assaults, as evidenced by the Daily Sun. This means P(B|A)/P(B) is less than 1, which means that P(A|B) is a lower value than P(A).

This means based on Bayes’ Law Cornell’s efforts should reduce the probability that sexual offences will occur on campus and that Cornell is placing security on it’s “broken windows”.


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October 2012