Books
A Criminologist’s Guide to R: Crime by the Numbers. Chapman & Hall/CRC The R Series
A Criminologist's Guide to R: Crime by the Numbers introduces the programming language R and covers the necessary skills to conduct quantitative research in criminology. By the end of this book, a person without any prior programming experience can take raw crime data, be able to clean it, visualize the data, present it using R Markdown, and change it to a format ready for analysis. A Criminologist's Guide to R focuses on skills specifically for criminology such as spatial joins, mapping, and scraping data from PDFs, however any social scientist looking for an introduction to R for data analysis will find this useful.
Key Features:
Introduction to RStudio including how to change user preference settings.
Basic data exploration and cleaning – subsetting, loading data, regular expressions, aggregating data.
Graphing with ggplot2.
How to make maps (hotspot maps, choropleth maps, interactive maps).
Webscraping and PDF scraping.
Project management – how to prepare for a project, how to decide which projects to do, best ways to collaborate with people, how to store your code (using git), and how to test your code.
Online version available at: https://crimebythenumbers.com/
Print version available to purchase: https://www.amazon.com/Criminologists-Guide-Crime-Numbers-Chapman/dp/1032244070
Published Peer-Reviewed Papers
2022
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Past research finds that stepparents harm and kill their partner's children at higher rates than biological parents do to their own children, a phenomenon called the “Cinderella effect.” Yet one major limitation of these studies is that reporting biases may account for a large share of the effect observed if reporting rates differ based on the victim-offender relationship. As abuse cases with serious injuries are more likely to be disclosed to police than ones with no injuries or minor injuries, using cases where the victim is seriously injured allows us to minimize the impact of differential reporting. Using data from the FBI's National Incident-Based Reporting System (NIBRS) which covers over 500,000 cases of child abuse from 1991 through 2019, we find that, relative to biological parents, unmarried partners, but not stepparents, are significantly more likely to seriously injure the child, partially supporting the Cinderella effect.
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Past research indicates that when professional sports games are played, crime increases. Yet, little is known about how playoff games affect crime. As many criminal events associated with sports games, such as riots, occur during playoff games, this is an important gap in the literature. Using data from 15 National Hockey League (NHL) teams from 2013 through 2019, we examine how assault, disorder, and property crimes change when playoff games are played at home relative to when they are played away. We find that during home games there are 7% more disorder crimes and 4% more property crimes than during away games which suggests that city responses to playoff hockey games should prioritize crime reduction strategies to improve public safety.
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What accounts for the steady decline in misdemeanour arrest rates in the United States following their peak in the mid-1990s? This article links the fluctuation in low-level law enforcement to changes in the budget and staffing resources cities devoted to policing. This materialist explanation contrasts with accounts that emphasize policy changes like the adoption of community policing. Dynamic panel regression analyses of 940 municipalities indicate low-level arrest rates declined most in places that reduced their police expenditure and personnel, net of crime and other controls. The adoption of community policing was unrelated to misdemeanour arrests. Findings suggest lawmakers should consider how increasing police budgets or police force sizes will likely be accompanied by increases in misdemeanour arrests and their attendant harms.
2021
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Research Summary
The notion that the unjustified use of force by police officers is concentrated among a few “bad apples” is a popular descriptor that has gained traction in scholarly research and achieved considerable influence among policy makers. 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% 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 4–6% reduction in the use of force incidents in Chicago over a 10-year period.
Policy Implications
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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Objectives
For more than one hundred years, street lighting has been one of the most ubiquitous capital investments in public safety. Prior research on street lighting is largely limited to ecological studies of very small geographic areas, creating substantial challenges with respect to both causal identification and statistical power. We address limitations of the prior literature by studying a natural experiment created by short-term disruptions to municipal street lighting.
Methods
We leverage a natural experiment created by the differential timing of the repair of nearly 300,000 street light outages in Chicago. By conditioning on street segment fixed effects and focusing on a short window of time around the repair of a street light outage, we can credibly rule out confounding factors due to area-specific time trends as well as street segment-level correlates of crime.
Results
We find that outdoor nighttime crimes change very little on street segments affected by street light outages, but that outages cause crime to spill over to nearby street segments. Effects are largest for robberies and motor vehicle theft.
Conclusions
Despite strong environmental and social characteristics that tend to tie crime to place, we observe that street light outages are sufficiently salient to disrupt longstanding patterns. While the impact of localized street light outages can reverberate throughout a community, the findings imply that improvements in lighting can be defeated by the displacement of crime to adjacent spaces and therefore do not necessarily suggest that localized investments in municipal street lighting will yield a large public safety dividend.
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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 shift 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. 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 one third in the first year after a gang takedown. Our estimates imply that 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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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 suggest that street lighting is a means through which policymakers can both control crime and improve community well-being.
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Objectives:
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.” In the large literature that has since proliferated, there remains considerable debate as to how crime concentration should be measured empirically. We suggest a measure of crime concentration that is simple, accurate and easily interpreted.
Methods:
Using data from three of the largest cities in the United States, we 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 considerably overstate the degree of crime concentration in a city.
Results:
While crime is significantly concentrated in a statistical sense and while some crimes are substantively concentrated among hot spots, the precise relationship is considerably weaker than has been documented in the empirical literature.
Conclusions:
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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Door locks are a 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 university campus. Using a difference-in-differences approach, this paper estimates the effect of card reader locks on crime in buildings. The results indicate that the locks do not significantly affect crime within buildings on a university campus.
2020
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Recent advances in forensic science, 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% and 75% accurate. Nevertheless, respondents still believe that forensic evidence is a key part of a criminal case, with nearly 30% of respondents believing that the absence of forensic evidence is sufficient for a prosecutor to drop the case and nearly 40% believing that the presence of forensic evidence – even if other forms of evidence suggest that the defendant is not guilty – is enough to convict the defendant.
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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 12 years between 2005 and 2016. Assaults disaggregated according to situation and extent of injury were employed as dependent variables. We 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, these results suggest 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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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 and punishment in criminal cases that involve forensic versus eyewitness testimony evidence and examining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) × 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 defendant should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the defendant to receive. 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.
2019
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Research Summary
The results reported in a large amount of the criminology literature reveal that hiring police officers leads to reductions in crime and that investments in police are an efficient means of crime control compared with investments in prisons. One concern, however, is that because police officers make arrests in the course of their duties, police hiring, albeit efficient, is an inevitable driver of “mass incarceration.” In this article, we consider the dynamics through which police hiring affects downstream incarceration rates.
Policy Implications
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 increase state prison populations markedly 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.