GEOG 510 DEATON Assignment 2: Homicides in Chicago INTRODUCTION

Transcription

1 GEOG 510 DEATON Assignment 2: Homicides in Chicago INTRODUCTION Of America s three largest cities (by population), Chicago has the highest violent crime and murder rate. i However, Chicago didn t make either of the FBI s 2015 top ten lists of big American cities with violent crime rates or murder rates ii. Due to sensationalized news reports, the world views Chicago through a tinted lens of crime reminiscent of its gangster past. With murder in Chicago on the rise, iii how much of this preconceived notion has a place in the global understanding of the city? The latest annual report by the Chicago Police Department would support the assumption as it determined that the leading assigned motive for murder is gang-relations (46.1%). A recent study showed that gang circumstances and the involvement of Hispanics, African Americans, and males increased the likelihood of homicides with non-normative characteristics in Chicago iv. This study calls for a deeper understanding of the factors that contribute to homicides, in addition to gang-relations. In a national climate of racial tension, unpacking the spatial distribution of homicide events by race will inform a more complete understanding of the city and differentiate the gang-stigma of the 1920s from the current epidemic. The objective of this study is to utilize crime and census data to describe the spatial distribution of homicide events in Chicago and to determine if the probability of homicide is higher in neighborhoods with specific racial compositions. In order to investigate this, several research elements were developed: The probability of daily homicides in Chicago (at least n and exactly n). The binomial distribution of homicides occurring from 0 to 10 days in Chicago. The frequency of daily homicides by neighborhood in Chicago. The probability of a homicide in a particular neighborhood with various proportions of white individuals versus various proportions of black individuals. METHODS The study is focused on the City of Chicago as shown in the greyed area in Figure 1 below. It is surrounded by suburban development to the South and West and Lake Michigan to the North and East. Chicago consists of 77 community areas that are divided into 25 police districts as overlaid in Figure 2. The maps used in this study were taken from the U.S. Census Bureau and the shapefiles are from the City of Chicago s Data Portal.

2 Figure 1: City of Chicago v Figure 2: Community areas and police districts vi The histogram displays the frequency of the number of homicides in one day in This is plotted with the number of homicides in each location. To develop this graphic, race and crime data were taken from the Chicago Police Department s Crime Data Portal and the U.S. Census Bureau s American Fact Finder website. The Chicago Police Department s Crime Data Portal is dedicated to promoting access to the government data and encouraging the development of creative tools to engage and serve Chicago s diverse community. vii The crime data was exported from the website as a comma-separated-values (.CSV) file for homicides occurring in Race information for Cook County (in which the City of Chicago is located) was downloaded from the U. S. Census Bureau s American Fact Finder website. Through an advanced search, the census tracts for Cook County were isolated and sorted by race with the latest dataset coming from 2014 (ACS 5-year estimates). This information was downloaded as a commaseparated-values (.CSV) file. The choropleth map displays the classes of population values for the total population, the population of white individuals, and the population of black individuals. The choropleth map is paired with a calculation of the number of homicides that took place in each census tract. The data from the histogram has been integrated with spatial data collected from the U.S. Census Bureau and the City of Chicago s Data Portal. The U.S. Census Bureau s (Maps and Data) TIGER products are spatial extracts from the Census Bureau s MAF/TIGER database, containing features such as roads, rivers, as well as legal and statistical geographic areas. viii Cartographic Boundary Shapefiles are simplified

3 representations of selected geographic areas specifically designed for small-scale thematic mapping. ix This map used the 2014 Cartographic Boundary Shapefiles for the state of Illinois downloaded as shape files (.SHP). Finally, The City of Chicago s Data Portal provided a shape file of the city boundary (to overlay). RESULTS The responses below inform an understanding of the spatial distribution of homicide events in Chicago and help to determine if the probability of homicide is higher in neighborhoods with specific racial compositions. The probability of at least one homicide occurring on any given day in Chicago is 69.9% as over the course of the year there were 255 homicides. To break that down further, the probability of at least 2-10 homicides occurring on any given day is shown below. 69.9% (n=1) 38% (n=2) 15.6% (n=3) 5.2% (n=4) 2.2% (n=5) 0.9% (n=6) 0.4% (n=7) 0.2% (n=8) 0.2% (n=9) 0% (n=10) To contrast, the probability of exactly one homicide occurring on any given day in Chicago is 31.5% as over the course of the year there were 115 days in which exactly one homicide occurred. To provide context to the information above, the probabilities of exactly 2-10 homicides occurring on any given day is shown below. 31.5% (n=1) 22.4% (n=2) 10.4% (n=3) 3.0% (n=4) 1.3% (n=5) 0.5% (n=6) 0.2% (n=7) 0% (n=8) 0% (n=9)

4 0.2% (n=10) The binomial distribution of at least 1 homicides occurring during a 10-day interval in Chicago is shown below: Binomial Distribution for 1 homicide occurring from 0 to 10 days in Chicago: Where, n = 10 days; x = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; p = 255/365 = 0.69; q = (1-p) = 0.31; n! = 10! (or 3,628,800). P(X) = n!p^(x)q^(n-x) X!(n-X)! Where X = 0, P(X) = (3,628,800)(0.69^0)(0.31^10) (0!)(10!) P(X) = (3,628,800)(1)( ) 3,628,800 P(0) = Where X=1, P(X) = (3,628,800)(0.69^1)(0.31^9) (1)(9!) P(X) = (3,628,800)(0.69)( ) 362,880 P(1) = Where X = 2, P(X) = (3,628,800)(0.69^2)(0.31^8) (2!)(8!) P(X) = (3,628,800)(0.476)( ) 80,640 P(2) = Where X = 3, P(X) = (3,628,800)(0.69^3)(0.31^7) (3!)(7!) P(X) = (3,628,800)(0.329)( ) 30,240

5 P(3) = Where X = 4, P(X) = (3,628,800)(0.69^4)(0.31^6) (4!)(6!) P(X) = (3,628,800)(0.2267)( ) 17,280 P(4) = Where X = 5, P(X) = (3,628,800)(0.69^5)(0.31^5) (5!)(5!) P(X) = (3,628,800)(0.156)(.00286) 14,400 P(5) = Where X = 6, P(X) = (3,628,800)(0.69^6)(0.31^4) (6!)(4!) P(X) = (3,628,800)(0.1079)(.00924) 17,280 P(6) = Where X = 7, P(X) = (3,628,800)(0.69^7)(0.31^3) (7!)(3!) P(X) = (3,628,800)(0.0744)(.0298) 30,240 P(7) = Where X = 8, P(X) = (3,628,800)(0.69^8)(0.31^2) (8!)(2!) P(X) = (3,628,800)(0.0514)(0.0961)

6 80,640 P(8) = Where X = 9, P(X) = (3,628,800)(0.69^9)(0.31^1) (9!)(1!) P(X) = (3,628,800)(0.0354)(0.31) 362,880 P(9) = Where X = 10, P(X) = (3,628,800)(0.69^10)(0.31^0) (10!)(0!) P(X) = (3,628,800)(0.0245)(1) 3,628,800 P(10) = The binomial analysis above can be summarized in Figure 4 below, which shows a distribution of homicides heavier in days 5 through 9. Probability P(X) Number of days of at least one homicide Figure 4: Binomial Distribution of Homicides

7 The frequency of daily homicides by neighborhood in Chicago as shown in Table 2 below indicates that the homicides are distributed across the geography of the city with a few (4) instances of significantly higher occurrence (over 5% frequency). CHICAGO NEIGHBORHOOD HOMICIDES IN A YEAR DAYS IN A YEAR DAILY FREQUENCY % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

8 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

9 Lastly, the probability of a homicide in a particular neighborhood with various proportions of white individuals versus various proportions of black individuals is dissected below in Tables 2 & 3. These numbers reflect an inversion of data across race, which means that Race has a relationship with homicides. Percent of African Americans in Neighborhood Probability of Homicide 0 to 10% 14.3% 10% to 20% 3.6% 30% to 40% 2.1% 40% to 50% 3.4% 50% to 60% 2.7% 70% to 80% 2.5% 80% to 90% 6.4% 90% to 100% 54.7% Table 2: Homicide in African American Neighborhoods Percent of Caucasian Americans in Neighborhood Probability of Homicide 0 to 10% 58.5% 10% to 20% 3.2% 30% to 40% 3.8% 40% to 50% 6.0% 50% to 60% 4.6% 70% to 80% 3.9% 80% to 90% 2.7% 90% to 100% 0.0% Table 3: Homicide in Caucasian Neighborhoods The histogram in Figure 3 below shows the number of homicides in one day over the course of the year This information tells that most homicides occur on different days. This may be an indication that the homicides are unique and unrelated events. Figure 3: Histogram Figure 4 below shows the spatial geography of homicides across the City of Chicago. This information tells that homicides occur with frequency at (41.9, ) and (41.75, ).

10 Figure 4: Locations of Homicides The cloropleth map (Figure 5) below shows locations of homicides in the City of Chicago against the race-content of each census tract. According to this map, homicides occur in census tracts with a higher proportion of African- Americans. The probability of a homicide occurring given the criteria is Locations of Homicides Figure 5: Cloropleth Map in which the blue-shade indicates density of African-Americans in the census tract.

11 DISCUSSION An analysis of the spatial and racial profiles of the City of Chicago show signs of a strong relationship. By importing homicide data from the Chicago Police Department, overlaying census tract data of neighborhood make-up, and compiling the information, it is possible to conclude that the racial profile of a neighborhood has influence over the frequency of homicide. Specifically, the findings show that as the neighborhood is made up of more African Americans, the quantity of homicides in a year increase. Conversely, as a neighborhood is made up of more Caucasians, the quantity of homicides in a year decreases. This data tells much about the characteristics and implies a relationship between these two qualities. However, it does not tell why. The study has yet to recommend or suggest reasons why the relationship is present. Certainly the political and economic geography play a large part. However, the reasoning for why the relationship exists is much more challenging to test and requires an in-depth analysis of qualitative factors. Many additional factors should be studied in conjunction with this research project to understand the nature of the relationship. Is it causal? If so, in which direction? Additionally, other races should be considered and mapped against the given data. REFERENCES i ii Ibid. iiihttps://portal.chicagopolice.org/portal/page/portal/clearpath/news/crime%20statistics/1_pdfsam_compstat%20public% %20Week%2013.pdf iv Varano, S. and Cancino, J. (2001) An Empirical Analysis of Deviant Homicides in Chicago. Homicide Studies. Vol. 5, No. 1, pg v vi vii viii ix Ibid.