Data for Change A Statistical Analysis of Police Stops, Searches, Handcuffings, and Arrests in Oakland, Calif., 2013-2014 Rebecca C. Hetey, Ph.D. Benoît Monin, Ph.D. Amrita Maitreyi, B.S. Jennifer L. Eberhardt, Ph.D. June 23, 2016 ! Copyright by Stanford SPARQ 2016 All Rights Reserved Suggested Citation: Hetey, R. C., Monin, B., Maitreyi, A., & Eberhardt, J. L. (2016). Data for change: A statistical analysis of police stops, searches, handcuffings, and arrests in Oakland, Calif., 2013-2014. Stanford University, SPARQ: Social Psychological Answers to Real-World Questions. 3 CONTENTS Executive Summary ..................................................................................................................................................... 9! Chapter 1: Stop Data Overview and Definition of Terms ........................................................................ 11! Our task ................................................................................................................................................... 11! Our approach .......................................................................................................................................... 11! Overview of the data .............................................................................................................................. 12! Type of stops ........................................................................................................................................... 13! Table 1.1. Stops by type ..................................................................................................................... 13! Who gets stopped? ................................................................................................................................. 13! Table 1.2. Stops by gender of person stopped ................................................................................. 14! Table 1.3. Stops by age group of person stopped ............................................................................ 14! Table 1.4. Stops by race of person stopped ...................................................................................... 15! Why are people stopped? ....................................................................................................................... 15! Table 1.5. Stops by reason for encounter ........................................................................................ 15! When are officers required to fill out a stop data form? .................................................................... 16! How do officers fill out each section of the stop data form? .............................................................. 17! Figure 1.1. General information section of stop data form ........................................................... 18! Figure 1.2. Section of stop data form containing information about encounter type and initial reason for encounter .......................................................................................................................... 19! Chapter 2: Methodology ........................................................................................................................................... 27! What is a benchmark? ............................................................................................................................ 30! What benchmarks have been used in past research? .......................................................................... 32! What role do benchmarks play in statistical models? ......................................................................... 40! Legitimate or illegitimate benchmark? ................................................................................................. 45! Our benchmarks ..................................................................................................................................... 49! Figure 2.1. A map of the correspondence between OPD police beats and police areas .............. 50! Overview of analyses .............................................................................................................................. 60! Chapter 3: Analysis of Stops .................................................................................................................................... 61! Core Findings .......................................................................................................................................... 61! Overview of the analyses presented in this chapter ............................................................................ 61! Description of Oakland’s census tracts ................................................................................................. 64! Figure 3.1. Histogram of tract populations ..................................................................................... 64! Figure 3.2. Share of overall stops attributable to tracts .................................................................. 65! What neighborhood characteristics predict the number of stops? ................................................... 66! 4 Figure 3.3. Histogram of raw distribution of stops by tract (left panel). Histogram of log transformed distribution of stops by tract (right panel) ................................................................ 67! Table 3.1. Pearson zero-order r correlation coefficient between number of stops made in census tract and characteristics of that tract .................................................................................... 68! Figure 3.4. Scatter plot of the association between violent crime rate and log transformed stops by tract ................................................................................................................................................. 69! Table 3.2. Results of regression models predicting log-transformed stops as a function of characteristics of the census tract in which the stop was made ..................................................... 70! “Overrepresentation” analysis ............................................................................................................... 72! Figure 3.5. A simulation of the percentage of African American stops that would be observed if police stop rates reflected neighborhood demographics ................................................................ 73! Figure 3.6. Scatterplots showing the association between the percentage of stops by race made in a census tract and the percentage of the racial group in question that lives in the tract ........ 74! Figure 3.7. Scatterplots showing the association between the number of African American stops made in a census tract and the percentage of African Americans who live in the tract, shown as a function of: the total number of stops made (left panel), the violent crime rate (middle panel), and the size of the tract (right panel) .................................................................... 74! Figure 3.8. A simulation of what percentage of African American stops would be observed if police stop rates reflected neighborhood demographics and police made more stops in African American neighborhoods (left panel). A scatterplot showing the association between the number of African American stops made in a census tract and the actual percentage of African Americans who live in the tract (right panel). Each blue dot represents a census tract, and the size of each dot is proportional to the number of stops in that census tract ................................ 76! Does the officer’s prior determination of race predict the number of stops? ................................... 77! Figure 3.9. A scatterplot showing the association between the number of African American stops made in a census tract and the percentage of African Americans who live in the tract as a function of whether race is not known by the officer prior to the stop (left panel) or is known prior to the stop (right panel) ........................................................................................................... 78! Chapter 4: Understanding the Post-Stop Outcome Analyses ................................................................ 79! How do we statistically test whether or not there are race differences in the post-stop outcomes? .................................................................................................................................................................. 79! How will the results of the post-stop outcome analyses be presented? ............................................ 81! Table 4.1. Control values of all covariates ....................................................................................... 84! Breakdown of moderator variables ...................................................................................................... 85! Table 4.2. Frequency of observed stops by area, race, and type of encounter ............................. 86! Table 4.3. Frequency of observed stops by area, race, and reason for encounter ....................... 87! Table 4.4. Frequency of observed stops by area, race, and special assignment ............................ 89! Chapter 5: Analysis of Handcuffing ................................................................................................................... 90! 5 Core Findings .........................................................................................................................................