Analyzing Patterns in Chicago Crime Data Peter Enns ([email protected]) and Mohit Iyyer ([email protected]) 10/10/2013 University of Maryland, College Park Tools used: Spotfire Dataset: We used the city of Chicago’s crime database, which catalogs all arrests made from 2001 to the present. It is publically available online at https://data.cityofchicago.org/PublicSafety/Crimes2001topresent/ijzpq8t2. This dataset has 5,350,430 arrest records, and each record has 21 attributes (e.g. date, location information, primary crime category). While this dataset is large, it is easy to filter out uninteresting categories using the online interface, which made loading the data into Spotfire easier. Available fields: ● Case Number ● Date ● Block ● IUCR (“Illinois Uniform Crime Reporting (IUCR) codes are four digit codes that law enforcement agencies use to classify criminal incidents when taking individual reports.”) ● Primary Type (e.g., Assault and Narcotics) ● Description ● Location Description ● Arrest (yes / no) ● Domestic (yes, no) ● Beat ● District ● Ward ● Community Area ● FBI Code ● X Coordinate ● Y Coordinate ● Year ● Update Date ● Latitude ● Longitude
● Location Findings: With some notable exceptions, crimes are committed more often during the summer. There is a large increase in most types of crime (e.g., assault, theft, and many others) during the summer in Chicago. This pattern is not apparent, however, in narcotics and prostitution offenses. This is not an artifact of a few summers with very high crime. By inspecting the rate of crimes from 2007 to 2012, a clear periodic pattern emerges. Interestingly, this pattern also shows up in where these crimes were committed. For example, most assaults occur on streets or sidewalks during the summer, but during the winter, a greater proportion of assaults occur in residences and apartments.
The crimes that do not exhibit strong seasonal patterns also do not show changes in where they are committed over the year. Narcotics offenses are roughly as likely to occur on a sidewalk or street during the winter as they are during the summer, and offenses related to prostitution are always likely to occur on the street.
In general, the crimes without pronounced seasonal effects seem to have more of a business nature than the other crimes. This makes sense because the demand for drugs or illegal sex will not change with the season. On the other hand, crimes like assault likely increase during the summer due to the simple fact that more people are interacting outside because the harsh Chicago winter is over, school is out, and many other reasons. Public shaming has been an effective tool to decrease prostitutionrelated crime overall, but is not a perfect solution Prostitution across all of Chicago dropped dramatically from 2005 to 2012. An overwhelmingly likely explanation for this pattern is that in late 2005, the Chicago police began making solicitor information available on the internet [1, 2].
However, if we focus our attention to two adjacent affluent regions in Chicago, The Loop (community area 8) and the adjacent Near North Side (community area 32), one type of crime related to prostitution, call operations, rose in popularity as public solicitation, the predominant type of prostitution, fell. Call operations refer to online or phonebased prostitution advertising. While public solicitation can be controlled by police patrols, online solicitation was and still is harder to track. Police can only catch call operation offenders in costly sting operations, so it is associated with less risk. It would seem that former public solicitors switched their mode of prostitution to avoid embarrassment after the 2005 policy was instituted. We were unable to determine if call operations were more expensive for “Johns” than public solicitation, but it would make sense given that we are seeing this pattern in richer neighborhoods. Loosening gun control laws has a negligible effect on Chicago’s murder rate.
In 2010, the US Supreme Court ruled that Chicago’s existing ban on all handguns, which was passed in 1985, was unconstitutional [3]. Since then, Chicago has loosened its gun control laws, which Second Amendment supporters claim will decrease murder rates. However, we found that this decision seems to have had no effect on Chicago’s murder rate. The above plot shows the number of murders committed every month from 2007 to now. Surprisingly, the murder rate has remained relatively constant over the past six and a half years. A linear regression confirmed this (slope=0.01 murders / month). Critique of Spotfire Positives: 1. In general, the filtering options were very robust and useful. 2. Trellising is exceedingly useful. At first, when we tried to look for changes in patterns from year to year, we used the filtering features. After gaining more experience, we started to make more trellises even if we didn’t plan to include the results in our report. It is a very convenient way to get a general idea of whether varying a field reveals interesting aspects of the dataset. 3. After finding an appropriate shapefile, plotting points on a map is very easy to do. Negatives:
1. Although the filtering features are very good, it would be helpful if there was an ‘uncheck all’ option for the check box filter view. As far as we could tell, this view is the easiest way to filter all but a small number of nonadjacent values at a time, but it is tedious to uncheck every single box. 2. The program crashes occasionally under normal use, and frequently when we tried to analyze the entire dataset at once. 3. It was unclear whether it was possible to save two related visualizations of different types in one image. This would have been useful for coordinated views. References 1. https://portal.chicagopolice.org/portal/page/portal/ClearPath/Online%20Services/Pr ostitution%20Arrests 2. http://query.nytimes.com/gst/fullpage.html?res=9F0CE3D61E3BF930A15755C0A9 639C8B63 3. http://en.wikipedia.org/wiki/McDonald_v._Chicago
