Research


Peer-Reviewed Journal Articles


2021

with Aaron Chalfin


The notion that the unjustified use of force by police officers is concentrated amongst a few ``bad apples" is a popular descriptor which has gained traction in scholarly research and achieved considerable influence among policymakers. But is removing the bad apples likely to have an appreciable effect on police misconduct? Leveraging a simple policy simulation and data from the Chicago Police Department, we estimate that removing the top 10 percent of officers identified based on ex ante risk and replacing them with officers drawn from the middle of the risk distribution would have led to only a 6 percent reduction in use of force incidents in Chicago over a ten-year period.
Our analysis suggests that surgically removing predictably problematic police officers is unlikely to have a large impact on citizen complaints. By assembling some of the first empirical evidence on the likely magnitude of incapacitation effects, we provide critical support for the idea that early warning systems must be designed, above all, to deter problematic behavior and promote accountability.


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with Aaron Chalfin and Mike LaForest


For more than one hundred years, street lighting has been one of the most enduring capitalinvestments to maintain public safety. In this study we provide a comprehensive examination of theeffect of street lights on crime, by estimating the effect of nearly 300,000 street light outages in Chicagoneighborhoods on crime. We find that outdoor nighttime crimes change very little on street segments affected by street light outages, but that crime appears to spillover to nearby street segments duringthese outages. These findings suggest that crime may follow patterns of human activity and that the impact of localized street light outages can reverberate throughout a community.


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with Aaron Chalfin and Maria Cuellar


In his 2014 Sutherland address to the American Society of Criminology, David Weisburd demonstrated that the share of crime that is accounted for by the most crime-ridden street segments is notably high and strikingly similar across cities, an empirical regularity referred to as the ``law of crime concentration."Using data from three of the largest cities in the United States, compare observed crime concentration to a counterfactual distribution of crimes generated by randomizing crimes to street segments. We show that this method avoids a key pitfall that causes a popular method of measuring crime concentration to overstate the degree of crime concentration in a city. Most (but not all) crimes are concentrated amongst a small number of hot spots but the precise relationship is weaker --- sometimes considerably so --- than has been documented in the empirical literature. Within a city, crime is least concentrated in the neighborhoods that experience the largest number of crimes. The law of crime concentration sometimes holds only tenuously in the communities in which crimes are most prevalent. The method we propose is simple and easily interpretable and compliments recent advances which use the Gini coefficient to measure crime concentration.


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with Aaron Chalfin


Observational evidence suggests that better ambient lighting leads people to feel safer when spending time outdoors in their community. We subject this finding to greater scrutiny and elaborate on the extent to which improvements in street lighting affect routine activities during nighttime hours. We report evidence from a survey experiment that examines individuals’ perceptions of safety under two different intensities of nighttime ambient lighting. Brighter street lighting leads individuals to feel safer and over half of survey respondents are willing to pay an additional $400 per year in taxes in order to finance a hypothetical program which would replace dim yellow street lights with brighter LED lights. However, poor lighting does not change people’s willingness to spend time outdoors or to engage in behaviors which mitigate risk. Results suggests that street lighting is a means through which policymakers can both control crime and improve community well-being.


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with Aaron Chalfin and Mike LaForest


During the last decade, while national homicide rates have remained flat, New York City has experienced a second great crime decline, with gun violence declining by more than 50 percent since 2011. In this paper, we investigate one potential explanation for this dramatic and unexpected improvement in public safety - the New York Police Department's rapid shift from a policy of mass enforcement, characterized by the intensive use of street stops and field interrogations, to a more surgical form of "precision policing”, in which law enforcement focuses resources on a small number of individuals who are thought to be the primary drivers of violence. In anticipation of a 2013 federal court ruling in which the NYPD's stop and frisk practices were found to be unconstitutional, the number of official street stops made by NYPD officers declined from a high of 680,000 in 2011 to just 12,000 just five years later. During the same period, the NYPD dramatically increased its investment in a different tactic -- targeted enforcement actions against criminal gangs, often centered around the City’s public housing communities. In this paper, we study New York City's campaign of "gang takedowns" in which suspected members of criminal gangs were arrested in highly coordinated raids and prosecuted on conspiracy charges. We show that gun violence in and around public housing communities fell by approximately 30 percent in the first year after a gang takedown. Our estimates imply that these coordinated gang takedowns explain nearly one quarter of the decline in gun violence in New York City's public housing communities over the last eight years.


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Door locks are an ubiquitous form of security to control access to a building with the goal of reducing crime there. However, research on door locks is often limited by methodological issues and primarily focuses on residential or commercial locations. This paper assesses the impact of card reader door locks on school buildings on an urban universitycampus. Using a difference-in-differences approach, this paper estimates the effect of cardreader locks on crime in buildings. The results indicate that the locks do not significantly affect crime within the buildings. Avenues for future research, including suggestions of specific universities at which to conduct further studies, are discussed.


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2020

with Shichun (Asminet) Ling and Colleen Berryessa


Recent studies have found that the general public perceives forensic evidence to be relatively inaccurate and to involve high levels of human judgement. This study examines how important the general public finds forensic evidence by comparing decisions on guilt andpunishment in criminal cases that involve forensic versus eyewitness testimony evidence andexamining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) x 4 (evidence type: DNA, fingerprint, victim eyewitness testimony, or bystander eyewitness testimony) - 1 (no victim testimony for murder scenario) design, yielding seven vignettes scenarios to which participants were randomly assigned. Results indicate that forensic evidence was associated with more guilty verdicts and higher confidence in a guilty verdict. Forensic evidence did not change the expected sentence length and did not generally affect the ideal sentence length. However, for rape, respondents believed that the offender should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the offender toreceive. The results of this study did not support a CSI effect. Overall, this study suggests that forensic evidence – particularly DNA – has a stronger influence during the verdict stage than the sentencing stage.


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with Li Sian Goh


Studies on the effect of marijuana on domestic violence often suffer from endogeneity issues. To examine the effect of marijuana decriminalization and medical marijuana legalization on serious domestic assaults, we conducted a difference-in-differences analysis on a panel dataset on NIBRS-reported assaults in 24 states over the twelve years between 2005 and 2016. Assaults disaggregated according to situation and extent of injury were employed as dependent variables. It was found that while the total number of assaults did not change, decriminalization reduced domestic assaults involving serious injuries by 18%. From a harm reduction perspective, the results suggested that while the extensive margin of violence did not change, the intensive margin measured by the seriousness of assaults were substantially affected by decriminalization. This result may be partially explained by reductions in offender alcohol intoxication and weapon-involved assault.


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with Shichun (Asminet) Ling and Maria Cuellar


Recent advances, especially the use of DNA technology, have revealed that faulty forensic analyses may have contributed to miscarriages of justice. In this study we build on recent research on the general public’s perceptions of the accuracy of 10 forensic science techniques and of each stage in the investigation process. We find that individuals in the United States hold a pessimistic view of the forensic science investigation process, believing that an error can occur about half of the time at each stage of the process. We find that respondents believe that forensics are far from perfect, with accuracy rates ranging from a low of 55% for voice analysis to a high of 83% for DNA analysis, with most techniques being considered between 65-75% accurate. Respondents still believe that forensic evidence is a key part of a criminal case with nearly 40% of respondents believing that the absence of forensic evidenceis sufficient for a prosecutor to drop the case and that the presence of forensic evidence, even if other forms of evidence suggest that the defendant is not guilty, is enough to convict thedefendant.


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2019

with Aaron Chalfin


A large literature establishes that hiring police officers leads to reductions in crime and that investments in police are a relatively efficient means of crime control compared to investments in prisons. One concern, however, is that because police officers make arrests in the course of their duties, police hiring, while relatively efficient, is an inevitable driver of "mass incarceration." This research considers the dynamics through which police hiring affects downstream incarceration rates. Using state-level panel data as well county-level data from California, we uncover novel evidence in favor of a potentially unexpected and yet entirely intuitive result --- that investments in law enforcement are unlikely to markedly increase state prison populations and may even lead to a modest decrease in the number of state prisoners. As such, investments in police may, in fact, yield a "double dividend'' to society, by reducing incarceration rates as well as crime rates.


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