Dr Jacob Kaplan

Dr Jacob Kaplan

Professional Specialist

Posts by Collection

publications

More Cops, Fewer Prisoners?

Published in Criminology & Public Policy, 2019

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.

Recommended citation: Kaplan, J & Chalfin, A. (2019). More Cops, Fewer Prisoners? Criminology & Public Policy, 18(1), 171-200.
Link to Publication

Public Beliefs About the Accuracy and Importance of Forensic Evidence in the United States

Published in Science & Justice, 2020

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.

Recommended citation: Kaplan, J, Ling, S & Cuellar, M. (2020). Public Beliefs About the Accuracy and Importance of Forensic Evidence in the United States. Science & Justice, 60(3), 263-272.
Link to Publication

Published in , 1900

The Importance of Forensic Evidence on Decisions of Criminal Guilt

Published in Science & Justice, 2021

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.

Recommended citation: Ling, S, Kaplan, J & Berryessa, C. (2021). The Importance of Forensic Evidence on Decisions of Criminal Guilt. Science & Justice, 61(2), 142-149.
Link to Publication

Measuring Marginal Crime Concentration: A New Solution to an Old Problem

Published in Journal of Research in Crime and Delinquency, 2021

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.

Recommended citation: Chalfin, A, Kaplan, J & Cuellar, M. (2021). Measuring Marginal Crime Concentration: A New Solution to an Old Problem. Journal of Research in Crime and Delinquency, 58(4), 467-504.
Link to Publication

Can Precision Policing Reduce Gun Violence? Evidence from “Gang Takedowns” in New York City

Published in Journal of Policy Analysis and Management, 2021

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.

Recommended citation: Chalfin, A, LaForest, M & Kaplan, J. (2021). Can Precision Policing Reduce Gun Violent? Evidence from "Gang Takedowns" in New York City. Journal of Policy Analysis & Management, 40(4), 1047-1082.
Link to Publication

Ambient Lighting and Perceptions of Public Safety: Evidence from a Survey Experiment

Published in Security Journal, 2022

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.

Recommended citation: Kaplan, J. & Chalfin, A. (2022). Ambient Lighting and Perceptions of Public Safety: Evidence from a Survey Experiment. Security Journal, 35, 694-724.
Link to Publication

Testing the Cinderella effect: Measuring victim injury in child abuse cases

Published in Journal of Criminal Justice, 2022

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.

Recommended citation: Block, K, & Kaplan, J. (2022). Testing the Cinderella effect: Measuring victim injury in child abuse cases. Journal of Criminal Justice, 82, 1019887.
Link to Publication

A Criminologist’s Guide to R: Crime by the Numbers

Published in Chapman & Hall/CRC The R Series, 2022

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.

Recommended citation: Kaplan, Jacob. (2022). "A Criminologist’s Guide to R: Crime by the Numbers" Chapman & Hall/CRC The R Series.
Link to Publication

Harm Reduction in Family Violence: Does Marijuana Make Assaults Safer?

Published in Journal of Interpersonal Violence, 2022

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.

Recommended citation: Kaplan, J & Goh, L.S. (2022). Harm Reduction in Family Violence: Does Marijuana Make Assaults Safer?. Journal of Interpersonal Violence, 37(7-8), NP5269-NP5293.
Link to Publication

An Analysis of National Hockey League Playoff Games and City-Level Crime Counts

Published in Crime & Delinquency, 2022

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.

Recommended citation: Block, K, & Kaplan, J. (2022). An analysis of National Hockey League playoff games and city-level crime counts. Crime & Delinquency, 69(11), 2194-2217.
Link to Publication

Street Light Outages, Public Safety and Crime Displacement: Evidence from Chicago

Published in Journal of Quantitative Criminology, 2022

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.

Recommended citation: Chalfin, A, Kaplan, J, & LaForest, M. (2022). Street Light Outages, Public Safety and Crime Displacement: Evidence from Chicago. Journal of Quantitative Criminology, 38, 891-919.
Link to Publication

The (In)Effectiveness of Campus Smart Locks for Reducing Crime

Published in Journal of Applied Security Research, 2023

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.

Recommended citation: Kaplan, J. (2023). The (In)Effectiveness of Campus Smart Locks for Reducing Crime. Journal of Applied Security Research, 18, 86-105.
Link to Publication

The Material of Policing: Budgets, Personnel, and the United States’ Misdemeanour Arrest Decline

Published in The British Journal of Criminology, 2023

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.

Recommended citation: Beck, B, Holder, E, Novak, A, & Kaplan, J. (2023). The Material of Policing: Budgets, Personnel, and the United States’ Misdemeanour Arrest Decline. The British Journal of Criminology, 63(2), 330-347.
Link to Publication

Political diversity in U.S. police agencies

Published in American Journal of Political Science, 2025

Partisans are divided on policing policy, which may affect officer behavior. We merge rosters from 99 of the 100 largest local U.S. agencies—over one third of local law enforcement agents nationwide—with voter files to study police partisanship. Police skew more Republican than their jurisdictions, with notable exceptions. Using fine-grained data in Chicago and Houston, we compare behavior of Democratic and Republican officers facing common circumstances. We find minimal partisan differences after correcting for multiple comparisons. But consistent with prior work, we find Black and Hispanic officers make fewer stops and arrests in Chicago, and Black officers use force less often in both cities. Comparing same-race partisans, we find White Democrats make more violent crime arrests than White Republicans in Chicago. Our results suggest that despite Republicans’ preference for more punitive law enforcement policy and their overrepresentation in policing, partisan divisions often do not translate into detectable differences in on-the-ground enforcement.

Recommended citation: Ba, B., Ge, H., Kaplan, J., Knox, D, Komisarchik, M., Lanzalotto, G., Mariman, R., Mummolo, J., Rivera, R., & Torres, M. (2025). Political diversity in U.S. police agencies. American Journal of Political Science. Online First.
Link to Publication

software

caesar (~909k downloads)

The goal of caesar is to encrypt and decrypt strings using a simple Caesar cipher or a pseudorandom number generation.

asciiSetupReader (~52k downloads)

Lets you open a fixed-width ASCII file (.txt or .dat) that has an accompanying setup file (.sps or .sas). These file combinations are sometimes referred to as .txt+.sps, .txt+.sas, .dat+.sps, or .dat+.sas. This will only run in a txt-sps or txt-sas pair in which the setup file contains instructions to open that text file. It will NOT open other text files, .sav, .sas, or .por data files. Fixed-width ASCII files with setup files are common in older (pre-2000) government data.

predictrace (~24k downloads)

Predicts the most common race of a surname and based on U.S. Census data, and the most common first named based on U.S. Social Security Administration data.

crimeutils (~18k downloads)

A collection of functions that make it easier to understand crime (or other) data, and assist others in understanding it. The package helps you read data from various sources, clean it, fix column names, and graph the data.

talks

teaching

Data Visualization Using R

Invited Lecture, Course: Statistics for the Social Sciences (Undergraduate), Department of Criminology, University of Pennsylvania, 2017

Data Visualization Using R

Invited Lecture, Course: Research Methods and Crime Analysis (Graduate), Department of Criminology, University of Pennsylvania, 2018

Data Visualization Using R

Invited Lecture, Course: Pro-seminar in Criminal Justice (Graduate), Department of Criminology, University of Pennsylvania, 2019

Crime Data in the United States

Invited Lecture, Course: Introduction to Methods of Research (Undergraduate), Department of Criminal Justice and Criminology, Sam Houston State University, 2022

Understanding FBI Crime Data

Invited Lecture, Course: Advanced Research Methods (Graduate), Department of Criminal Justice and Criminology, Sam Houston State University, 2022

R for Crime Research

Workshop, Department of Criminal Justice and Criminology, Sam Houston State University, 2023

Current Issues in Policing

Invited Lecture, Course: Contemporary Issues in Criminal Justice (Graduate), Law and Justice Studies Department, Rowan University, 2024

Survey Data Analysis With R: A Three-Day Academic Workshop

Workshop, Criminal Justice @ SPIA, Data-Driven Social Science & and Survey Research Center, Princeton University, 2025

This three-day R workshop is designed for beginners to develop the skills necessary to quantitatively analyze data. Participants will learn how to use the programming language R to explore and manipulate datasets, focusing on real-world applications in social sciences. The workshop covers fundamental skills such as identifying issues with the data, cleaning the data by filtering, standardizing, and fixing issues in the data, visualizing descriptive statistics, and documenting every part of this process. Each day concludes with practical exercises, and participants will leave with the skills to convert raw data into useful information. While these skills can be used in many social science fields, this workshop focuses on topics most commonly used for quantitative research of criminal justice topics. The data used will also introduce students to some of the most common data used by criminal justice researchers and practitioners.

How Reliable is Crime Data?

Invited Lecture, Course: The Politics of Policing (Undergraduate), Politics Department, Princeton University, 2025

Invited Lecture on how reliable administrative FBI crime data is for research.

Data Cleaning and Analysis with R

Workshop, SPI 300 S06 – Policing in the United States, Princeton University, 2025

This one-day R workshop is designed for beginners to develop the skills necessary to quantitatively analyze data. Participants will learn how to use the programming language R to explore and manipulate datasets, focusing on real-world applications in social sciences. The workshop covers fundamental skills such as identifying issues with the data, cleaning the data by filtering, standardizing, and fixing issues in the data, visualizing data and making descriptive statistics.

Web Scraping with R

Workshop, Program for Quantitative and Analytical Political Science, Princeton University, 2025

This workshop teaches graduate students how to web scrape with R using the rvest and RSelenium packages. This covers web scraping static websites, responsible practices for web scraping, and introduces web scraping dynamic pages using RSelenium.

How Reliable is Crime Data?

Invited Lecture, Course: Criminal Justice Research (Undergraduate), Law and Justice Studies Department, Rowan University, 2025