Diffusion of Homicides from Illegal Firearm Markets

Jeffrey Fagan Garth DaviesColumbia University Simon Fraser University

This Research Extension of theory and research on social

contagion to the case of gun violence and gun markets

Identify epidemic patterns Isolate effects of gun markets as sources

of “pathogen” that both weakens host susceptibility and directly increases disease risk – in this case, gun violence

Locate highest risk areas

Social Contagion Diffusion: the spread of abstract ideas and

concepts, technical information, and practices within a social system

The S-Curve revised (Godin, Rogers)

Examples of Social Contagion• Diffusion of Innovation

• Corn Seed Experiments (Ryan and Neal)­ Adaptation of Tetracyclene (Coleman, Burt)

• Consumer Behavior and Cultural Adaptations (Gladwell)­ Fashion, Music

• Political Thought• Language• Problem behaviors (Rowe and Rogers)

­ Teenage Pregnancy, Smoking, Drug and Alcohol Use­ School Dropout­ Suicide

• Lynchings (Tolnay, 1998)• Riots (Short)• Gang homicides (Papachristos, 2005)

Mechanisms of Social Contagion Network interactions (Burt, Kandel)

egos interact at points of contact between innovator and adaptor homogeneity and density of social networks dictates patterns of contact

and social interaction (homophily) Information obtained from close peers located in social and organizational

networks has more weight than information obtained from objective sources

Cultural software (Balkin) memetics within social networks: spread of beliefs and ideas via

competition of ideas and survival of fittest, social norms transmission Behavioral scripts (Fagan and Wilkinson, Nisbitt)

Practice and reinforcement of contingent behavioral responses Infectious disease model of contagion Most work on individuals and social networks, with

attention to social context as facilitating transmission within networks, Less on contagion across social areas Lynching, Homicide research – across larger aggregates

Illicit Gun Markets and Violence

Recent evidence Braga and Pierce (2005) – disrupting gun markets

reduces gun availability But generally little research on firearm violence

epidemiology and proximity to sources of illegal guns Some qualitative evidence using small areas to

approximate local markets Difficulties in identifying spatial and economic

parameters of these markets In this research, we use localized measures of

gun seizures to approximate location and intensity of illegal gun availability

Litigation Interest Municipal and private lawsuits Convergence of criminal and tort responsibility Theories

Public nuisance Product liability “Toxic tort” theory

Proximal causation risk of death following exposure to firearms

Gun litigation as a privatized form of risk regulation

Data SourcesGun Seizures

BATF Trace Data, New York City Extract, geocoded to seizure location, FOIA Extract dated February 15, 2002; Bureau of Alcohol, Tobacco and Firearms NAACP Extract dated September 13, 2002

Homicide and Assault

NYC Dept of Health, Injury Surveillance SystemVital Statistics records of deaths geocoded to census tract of victim residenceSPARCS hospital admissions records for intentional injuries, geocoded to patient residenceICD10 codes for firearm injuries

Social and Economic Composition

New York City Department of City Planning, PL 94-171 Redistricting File and Summary File for 1990 and 200 U.S. Census, tracts reconciled to 1990 boundaries

Figure 1 Gun and Non-Gun Homicides, New York City, 1968-2000

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Table 1. Homicide and Assault Counts and Rates, New York City Census Tracts, 1996-2000 1996 1997 1998 1999 2000 2001 2002

Counts

ATF Gun Seizures 822 6305 3192 2509 3033 2704 1565

Total Homicide 852 715 569 634 648 609 544

Gun Homicide 580 445 341 367 413 346 325

Total Assault 6038 5462 5384 5126 5037

Gun Assault 1081 846 806 810 789

Rates (per 100,000)

ATF Gun Seizures 11.98 97.74 50.77 40.75 40.29 54.09 27.59

Total Homicide 10.94 9.16 7.27 8.04 7.79 7.97 6.83

Gun Homicide 7.67 5.85 4.34 4.38 5.05 4.44 4.09

Total Assault 92.46 80.83 79.24 78.71 77.04

Gun Assault 14.94 12.56 12.82 11.89 10.94

Source: New York City Department of Health and Mental Hygiene, Division of Epidemiology, various years; Bureau of Alcohol, Tobacco and Firearms Trace Data, FOIA Extract dated February 15, 2002; Bureau of Alcohol, Tobacco and Firearms NAACP Extract dated September 13, 2002; New York City Department of City Planning, PL 94-171 Redistricting File and Summary File 3 (STF3a) of the 1990 and 2000 U.S. Census.

Table 2. Correlations between Gun Homicides, Gun Assaults, and Gun Seizures, by Census Tract, New York City, 1996-2000, Correlations (Pearson Correlation Coefficients, Two-Tailed Significance Test)a

ATF Gun Seizures

Total Homicides

Gun Homicides

Total Assaults

ATF Gun Seizures --

Total Homicides .715** --

Gun Homicides .690** .936** --

Total Assaults .698** .709** .666** --

Gun Assaults .669** .698** .676** .840**

Source: New York City Department of Health and Mental Hygiene, Division of Epidemiology, various years; Bureau of Alcohol, Tobacco and Firearms Trace Data, FOIA Extract dated February 15, 2002; Bureau of Alcohol, Tobacco and Firearms NAACP Extract dated September 13, 2002; New York City Department of City Planning, PL 94-171 Redistricting File and Summary File 3 (STF3a) of the 1990 U.S. Census.

Table 3. Descriptive Statistics for Injury, Fatality, and Census Tract Social and Economic Characteristics, New York City Census Tracts: 1990 Census Data

Valid N of

Census Tracts

Mean Standard Deviation

Social and Economic Characteristics

% Households with Public Assistance Income 1969 14.05 12.92

Gini Index of Income Inequality for Total Household Income 1969 0.38 0.08

% Households Under Poverty Level 1969 18.35 14.59

% High School Graduates - Total - 25+ 1971 66.20 15.78

% Employed in Managerial, Professional, or Technical Jobs 1970 29.63 14.89

% Employed Total 1970 90.25 6.49

% in Labor Force 1971 60.79 10.03

% Female Headed Households with Children < 18 years 1969 10.27 10.07

% Nonwhite 1971 55.52 36.08

Racial Fragmentation Indexa 1971 0.38 0.19

Supervision Ratio (25-64 by 5-24) 1971 0.53 0.36

%Youth Population (5-15) 1971 14.91 6.33

% Foreign Born 1971 27.66 14.88

Linguistic Isolation - % Homes with no English Speaker 1971 11.23 9.94

Residential Mobility - % Living in Same House as 1985 1971 63.50 10.16

% Occupied Units that are Rentals 1969 65.80 25.37

Total Population – 1990 1971 3691 2863

Source: New York City Department of City Planning, Summary File 3 (STF3a) of the 1990 U.S. Census.

Table 4. Factor Scores, New York City Census Tracts, 1990 and 2000

1990 2000

Variable Weight

Eigen-value

% Variance

Variable Weight

Eigen-value

% Variance

Poverty/Inequality 5.60 69.94 5.50 68.71

% Households Below Poverty Level 0.93 0.92

% Households with Public Assistance Income 0.93 0.88

% Less Than High School Graduates 25+ 0.90 0.89

Gini Index Total Household Income Inequality 0.86 0.87

% FHH w/ Children < 18 0.86 0.83

% Unemployed 0.77 0.77

% Not Employed Mang’l, Prof’l, or Tech Jobs 0.74 0.75

% Not in Labor Force 0.67 0.69

Segregation 1.29 64.59 1.17 58.39

Racial Fragmentation Indexa 0.80 0.76

% Nonwhite 0.80 0.76

Supervision 1.59 79.45 1.69 84.30

%Youth Population (5-15) 0.89 0.92

Supervision Ratio (25-64 by 5-24) 0.89 0.92

Immigration 1.54 76.89 1.56 78.08

% Homes with no English Speaker 0.88 0.88

% Foreign Born 0.88 0.88

Housing Stability 1.31 65.62 1.32 66.00

% Living in Same House as 5 Years Ago 0.81 0.81

%Occupied Units that are Rentals 0.81 0.81

Source: New York City Department of City Planning, Summary File 3 (STF3a) of the 1990 U.S. Census. a. For the computation of racial fragmentation, see: Charles Lewis Taylor & Michael C. Hudson, World Handbook of Political and Social Indicators 216 (1972). Racial fragmentation is a measure of the racial heterogeneity within an area, and is computed as: 1 - ((P)2), where P = proportion of each race within the spatial unit.

Figures 1 and 2. Gun Seizures and Gun Homicides,New York City Census Tracts

1997 and 2002

Analysis Estimate models of gun seizures for each year in panel, use

residuals as measures of gun market intensity (lagged) We don’t think of gun markets as a tx, which would call for a different

analytic strategy Estimate spatial lag for adjacent census tracts, controlling for

second-order diffusion beyond immediate diffusion area Include social structure both in estimation of gun markets and

in homicide models (we use residuals of gun seizures) Models estimated using mixed effects poisson regressions

with AR(1) covariance, random intercepts and random effects for time See, Singer and Willett (2004), Rabe-Hesketh, S., Skrondal, A. and

Pickles, A. (2005)

Violence

Gun MarketFactors

Violence

Gun MarketFactors

Tract

Neighborhood

Second Order Neighborhood

1.

Table 5. Mixed Effects Poisson Regression of Gun Seizures by Neighborhood Social Structure, New York City Census Tracts, 1996-2002 Effect Est. t

Intercept -5.380

-23.54** Time -.080 -11.33** Population (Logged) .682 24.63** Poverty .630 13.96** Segregation .117 3.25** Social Control -.1719 -3.53** Immigration -.311 -11.35** Housing .207 5.75** Time Interactions

Poverty .005 .45 Segregation .006 .65 Social Control .018 1.63 Immigration -.019 -2.87** Housing -.020 -2.34*

-2 Log Likelihood 53355

p(t) * p < .05, ** p < .01

Table 6. Mixed Effects Poisson Regression of Gun Seizures (lagged residuals) on Four Violence Measures (Slope Effects only), New York City Census Tracts, 1996-2002a

Total

Homicide Gun

Homicide Total

Assault Gun

Assault Interaction of Time with: Est. t Est. t Est. t Est. t

Gun Seizures, Lagged Residuals .005 4.16 ** .005 3.34 ** .001 0.61 .005 1.59 Second Order Spatial Lag -.017 -1.18 -.018 -0.73 .000 -0.03 .080 4.79 ** Poverty .000 -0.01 .008 0.53 -.007 -0.72 -.003 -0.15 Segregation .004 0.48 .014 1.42 -.016 -2.81 ** -.038 -2.81 ** Social Control .036 2.88 ** .017 1.07 .020 2.05 * .001 0.04 Immigration -.034 -6.15 ** -.047 -6.63 ** .016 3.66 ** -.024 -2.43 * Housing -.020 -2.22 * -.038 -3.35 ** .007 0.96 .034 2.27 *

-2 Log Likelihood 31743.3 37652.4 8883.3 21328

a. Assault measures 1996-2000 only p(t): * p < .05 ** p < .01

Quartiles

1 2 3 4

Total Homicide 1.89 2.53 4.26 8.82Gun Homicide 2.48 2.00 4.47 8.56Total Assault 1.39 2.52 4.21 9.38Gun Assault 1.77 2.39 4.03 9.31

Quartiles

1 2 3 4

Total Homicide 0.38 0.56 0.94 1.50Gun Homicide 0.20 0.33 0.59 0.98Total Assault 3.47 4.74 7.46 12.58Gun Assault 0.39 0.61 1.19 2.37

Mean Gun Seizure Rates per 10,000 Persons by Violence

Quartiles

Mean Violence Rates per 10,000 persons in Surrounding Tracts

by Gun Seizure Quartiles

Table 7. Gun Seizure and Violence Rates by Quartiles, New York City Census Tracts, 1996-2002

Figure 3. Gun Seizure Rates per 10,000 Persons for Four Violence Indices

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Figure 4. Violence Rates by Gun Seizure Quartiles, New York City Census Tracts, 1996-2002

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Table 8. Mixed Effects Poisson Regression of Gun Seizures on Four Violence Measures by Gun Seizure Quartile (Slope Estimates Only), New York City Census Tracts, 1996-2002a

1 2 3 4 Model Est. t Est. t Est. t Est. t 1. Total Homicide .005 .52 -.008 -.91 .010 3.06 ** .004 2.78 ** 2. Gun Homicide .005 .30 .001 -.08 .007 1.80 * .004 2.47 ** 3. Total Assault -.001 -.93 .007 1.29 -.0003 -0.11 .0004 .22 4. Gun Assault -.029 -1.12 -.017 -1.25 -.009 -1.11 -.006 1.56 a. Assault measures 1996-2000. All estimates controlled for main effects, spatial lag, and five social structural factors p(t): * p < .05 ** p < .01

Table 9. Repeated Measures ANOVA on Predicted Group Means across Gun Seizure Quartiles, New York City Census Tracts, 1996-2002 Total Homicide

Quartile 1 2 3 4 1 - 2 .110** - 3 .280** .170** - 4 .334** .224** .054 -

Gun Homicide

Quartile 1 2 3 4 1 - 2 .154** - 3 .394** .191** - 4 .449** .295** .104 -

p(F): ** p < .01 * p < .05

Conclusions Evidence of contagious effects from illegal gun

markets, as measured by gun seizures, on gun homicide and total homicide Weaker evidence for assaults

Effects concentrated at extremes of gun markets and at concentrations of “susceptibility”

Assaults are more heterogeneous, not closely linked to of gun markets

Quarantine v. Innoculation Policies to disrupt gun markets should have payoffs Distributive justice perspective points to innoculation as

preferable strategy (Markovits, 2005)