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

ratesii. 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 Chicagoiv. 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.

Figure 1: City of Chicagov Figure 2: Community areas and police districtsvi

The histogram displays the frequency of the number of homicides in one day in 2015. 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 2015. 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 comma-

separated-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

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)

• 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)(.0000082)

3,628,800

P(0) = 0.000082

Where X=1,

P(X) = (3,628,800)(0.69^1)(0.31^9)

(1)(9!)

P(X) = (3,628,800)(0.69)(.000026)

362,880

P(1) = 0.0001794

Where X = 2,

P(X) = (3,628,800)(0.69^2)(0.31^8)

(2!)(8!)

P(X) = (3,628,800)(0.476)(.000085)

80,640

P(2) = 0.0018207

Where X = 3,

P(X) = (3,628,800)(0.69^3)(0.31^7)

(3!)(7!)

P(X) = (3,628,800)(0.329)(.0000275)

30,240

P(3) = 0.0010857

Where X = 4,

P(X) = (3,628,800)(0.69^4)(0.31^6)

(4!)(6!)

P(X) = (3,628,800)(0.2267)(.0008875)

17,280

P(4) = 0.042251

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) = 0.1124

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) = 0.2094

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) = 0.2661

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)

80,640

P(8) = 0.2223

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) = 0.1099

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) = 0.0245

The binomial analysis above can be summarized in Figure 4 below, which shows a distribution of homicides heavier in

days 5 through 9.

Figure 4: Binomial Distribution of Homicides

Prob

abilit

y P(

X)

Number of days of at least one homicide

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

1 6 365 1.64%

2 4 365 1.10%

3 12 365 3.29%

4 1 365 0.27%

5 0 365 0.00%

6 1 365 0.27%

7 0 365 0.00%

8 1 365 0.27%

9 0 365 0.00%

10 0 365 0.00%

11 1 365 0.27%

12 0 365 0.00%

13 0 365 0.00%

14 5 365 1.37%

15 2 365 0.55%

16 7 365 1.92%

17 0 365 0.00%

18 1 365 0.27%

19 8 365 2.19%

20 0 365 0.00%

21 2 365 0.55%

22 8 365 2.19%

23 18 365 4.93%

24 5 365 1.37%

25 50 365 13.70%

26 15 365 4.11%

27 16 365 4.38%

28 10 365 2.74%

29 23 365 6.30%

30 13 365 3.56%

31 4 365 1.10%

32 2 365 0.55%

33 2 365 0.55%

34 1 365 0.27%

35 3 365 0.82%

36 3 365 0.82%

37 3 365 0.82%

38 7 365 1.92%

39 4 365 1.10%

40 4 365 1.10%

41 0 365 0.00%

42 8 365 2.19%

43 17 365 4.66%

44 23 365 6.30%

45 2 365 0.55%

46 12 365 3.29%

47 3 365 0.82%

48 2 365 0.55%

49 18 365 4.93%

50 0 365 0.00%

51 1 365 0.27%

52 1 365 0.27%

53 14 365 3.84%

54 3 365 0.82%

55 4 365 1.10%

56 1 365 0.27%

57 1 365 0.27%

58 5 365 1.37%

59 1 365 0.27%

60 3 365 0.82%

61 17 365 4.66%

62 3 365 0.82%

63 8 365 2.19%

64 0 365 0.00%

65 0 365 0.00%

66 10 365 2.74%

67 18 365 4.93%

68 21 365 5.75%

69 18 365 4.93%

70 6 365 1.64%

71 12 365 3.29%

72 0 365 0.00%

73 9 365 2.47%

74 0 365 0.00%

75 6 365 1.64%

76 1 365 0.27%

77 2 365 0.55%

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

Probabil ity 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

Probabil ity 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 2015. 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, -87.74) and (41.75, -87.60).

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 0.2597.

Figure 5: Cloropleth Map in which the blue-shade indicates density of African-Americans in the census tract.

Locations of Homicides

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 http://chicago.cbslocal.com/2015/10/22/violent-crime-statistics-for-every-city-in-america/ ii Ibid. iiihttps://portal.chicagopolice.org/portal/page/portal/ClearPath/News/Crime%20Statistics/1_pdfsam_CompStat%20Public%202016%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. 5-29. v https://data.cityofchicago.org/Facilities-Geographic-Boundaries/Boundaries-City/ewy2-6yfk vi https://arrestjustice.files.wordpress.com/2011/06/chicago-police-district-map-community-areas.jpg vii http://www.cityofchicago.org/city/en/narr/foia/CityData.html viii https://www.census.gov/geo/maps-data/data/cbf/cbf_tracts.html ix Ibid.