Downloaded by guest on October 2, 2021 www.pnas.org/cgi/doi/10.1073/pnas.1814773116 a Yokum David of cameras effects body-worn the police evaluating trial control randomized A ohv vdnir au,bt o nenlafisadcriminal and affairs internal for 16). (15, both investigations value, expected captur- evidentiary also By are have (15). cameras to the occurs interaction, violence police–civilian the that ing involved likelihood parties the all calm reduce to and predicted “civilizing are so-called BWCs a mecha- wherein exact to effect,” the allude Whatever sometimes two. commentators the nisms, of combination being a of or threat caught, heightened behavior self-awareness, and greater BWCs include to linking could underlying mechanisms likely The psychological less behavior. or be combative social or may inappropriate officer civilians miscon- in Similarly, BWC-equipped engage or deter (14). a force behavior with and of interacting unprofessional use protocols unjustified in especially departmental duct, engaging to from adherence police officer age acceptable socially with monitoring alignment settings, conduct. into these behavior shift Across turnout to (13). voter promot- appears theft stimulating (10), reducing (11), and rules honesty (12), believe recycling encouraging to and they adherence to productivity ing when work (6–9) increasing (5), differently giving from Works charitable act watched, dat- Hawthorne being research, people at are of they that experiments range classic suggested wide the A has under to camera. if civil- a back differently of and ing themselves lens comport officers watchful may Both the street behavior. the on on ians effects anticipated and their practices police 4). to (3, document disputes solution to resolve technological to least a behavior at civilian as or BWCs policing, have equip Civil Matter improve to American Lives shared police Black the the and and urged as video Zero, Campaign such bystander Union, Stakeholders in Liberties media. captured social were across shootings, which to officer-involved of high-profile, intend police of many been series has large or expansion a the of by of implemented motivated Much 95% (2). already program that BWC a have found implement survey either nationwide country departments the a support throughout to and programs funding (1), BWC in million of $23 implementation over the awarded Justice of ment P cameras body-worn DC. Washington, contexts in to particularly induce similar policing, other to suggest in ability as changes results BWCs’ behavioral of well large-scale These expectations as our outcomes. recalibrate complaints, should judicial civilian we and and effects activities force insignificant show of statistically policing we use and Here small police DC. very on have Washington, BWCs in that officers Department con- Metropolitan we 2,224 Police involving BWCs, their trial of controlled of effects randomized evidence a the ducted yet estimate To institutions, limited. legal is effectiveness and perceived police the of and policing legitimacy 2018) improve 28, as to August promoted mechanism review widely for technological been (received a have 2019 (BWCs) 21, cameras March approved body-worn and Police MA, Cambridge, University, Harvard Murphy, A. Susan by Edited and 48109; MI Arbor, Ann Michigan, of University Program, 02912; h a C fc fteCt diitao,EeuieOfieo h ao,Wsigo,D 20004; DC Washington, Mayor, the of Office Executive Administrator, City the of Office DC, @ Lab The nteplcn otx,cmrsaeepce oencour- to expected are cameras context, policing the In to part, large in due, is BWCs for support widespread The lc oywr aea(W)porm r rapidly are Depart- US the programs 2015, In (BWC) States. United the camera across spreading body-worn olice c xctv fc fteCifo oie erpltnPlc eatet ahntn C20024; DC Washington, Department, Police Metropolitan Police, of Chief the of Office Executive a,b,1,2 | edexperiments field nt Ravishankar Anita , | policing a,c,d,1 n lxne Coppock Alexander and , e eateto oiia cec,Yl nvriy e ae,C 06511 CT Haven, New University, Yale Science, Political of Department ulse nieMy7 2019. 7, May online Published 1073/pnas.1814773116/-/DCSupplemental. y at online information supporting contains article This 2 1 siae ftetetetefcshv endpstdi h pnSineFramework, Science Open the in deposited been https://osf.io/p6vuh/. have difference-in-means effects the treatment reproducing the for of sufficient estimates dataset cleaned The deposition: Data the under Published Submission.y Direct PNAS a research, is article This performed interest.y of research, conflict no declare designed authors The A.C. paper.y the and wrote and A.R., data, analyzed D.Y., contributions: Author oisplc oc,apoiaeyhl falfl uypto n station and patrol duty full all of half the approximately evaluate BWCs force, of Dis- to deployment police RCT MPD’s the of its an part of implement to as Specifically, and Department citywide. design BWCs Police of to effects (MPD) Metropolitan Columbia the of trict with collaborated We the Methods introduce that 27). (14, assignments spillover random within-officer for shift-level sam- potential small or treat- either by sizes limited detectable been ple typically no has RCTs found The of (26). set outcomes trials extant measured Cam- on Further 25). differences but control 25). (24, versus experiments ment others (16, some at in others it complaints use not decrease decrease police and to increase Kingdom appeared sites to eras some United appeared at the BWCs force of in States, of series sites United a the In several and results. across mixed conducted with RCTs conducted, been have BWCs randomly if as were BWCs conditioning covariates, after pretreatment that, assigned. of believe set to outcomes. a need potential on would of we independent particular, is In treatment adjustments the statistical on made, after depend are studies whether, those about in assumptions drawn strong inferences (15, com- causal without The those studies to 23). Other BWCs 22, wear 21). to of happened (20, introduction who department officers the pared police after and the before into officers BWCs compar- of by behavior BWCs the evaluated ing (17–19). have limited studies relatively observational remains Several outcomes policing on effects owo orsodnesol eadesd mi:david Email: addressed. be should correspondence work.y whom To this to equally contributed A.C. and A.R., D.Y., n s ffre ecnld htteefcso aea are cameras hoped. of have effects many the affect than that smaller conclude likely meaningfully We complaints Our force. including not of data. outcomes, use of administrative and did range a using cameras on mo behavior police that 7 of indicate minimum results behav- a police to subsequent for officers tracked ior We assigned not. randomly or we cameras receive DC), Depart- Washington, Police in Metropolitan the ment field of large-scale officers a (2,224 In experiment interactions. civilian–police hopes improving in of cameras body-worn adopting are departments Police Significance ml ubro admzdcnrle ras(Cs of (RCTs) trials controlled randomized of number small A anticipated the have BWCs whether on evidence existing The e,1 PNAS y NSlicense.y PNAS | b h oiyLb rw nvriy rvdne RI Providence, University, Brown Lab, Policy The d a 1 2019 21, May ulcPlc n oiia cec on PhD Joint Science Political and Policy Public | o.116 vol. www.pnas.org/lookup/suppl/doi:10. | [email protected]. o 21 no. | 10329–10332 y
SOCIAL SCIENCES officers were randomly assigned to wear BWCs, while the other half We also disaggregated the complaints by disposition: sustained, not remained without BWCs. With 2,224 MPD members participating in the trial, sustained, or unresolved due to insufficient facts. this study is the largest randomized evaluation of BWCs conducted to date. iii) The policing activity category included traffic tickets and warnings Our project was deemed “not human subjects research” by the Yale Univer- issued, reports taken from particular types of calls for service, arrests sity IRB (protocol no. 2000020390), as all study activities were carried out on specific charges (e.g., disorderly conduct, traffic violations, assaults by MPD. against a police officer), and injuries sustained by officers in the line of The primary outcomes of interest were documented uses of force and duty. We used these measures to evaluate the effects of BWCs on officer civilian complaints, although we also measure a variety of additional discretion and activity, as well as on civilian behavior. policing activities and judicial outcomes. All outcomes were measured iv) Finally, we examined the effects of BWCs on judicial outcomes, mea- using administrative data. Before obtaining outcome data, we developed sured by whether MPD arrest charges are prosecuted by the US a detailed write-up of the methodology and planned statistical analyses Attorney’s Office (USAO) or the Office of the Attorney General (OAG) (a preanalysis plan) and publicly shared it on the Open Science Framework. and the disposition of those charges. Our examination of this set of The preanalysis plan is included in SI Appendix. outcomes was constrained by limitations in the available data. Namely, Our study encompassed the entire department and included geographic we did not have access to the full datasets managed by the USAO, OAG, coverage of the entire city. We identified eligible officers within each of the and the courts. We instead had access to a subset of these data available seven police districts (as well as several specialized units) based on the fol- to MPD, which captures only the initial charges on which an individual lowing criteria: The officer was on active, full duty administrative status and was arrested. A consequence is that we were unable to track court out- did not have a scheduled leave of absence during the study period, held comes for any changes to those initial charges. As this limitation applies a rank of sergeant or below, and was assigned to patrol duties in a patrol to both control and treatment groups, however, we were still able to district or to a nonadministrative role at a police station. Eligible officers conduct a preliminary analysis on the evidentiary value of BWCs. within each district or special unit were then randomly assigned to one of Due to logistical constraints, MPD deployed cameras on a district-by- two groups: ( ) no BWC (control) or ( ) with BWC (treatment). Specifically, i ii district basis over the course of 11 mo. Officers in two of the seven police treatment entails assignment of an eligible participant to wear and use a districts received cameras in late June 2015, with the deployment to the BWC in accordance with MPD policy. MPD General Order SPT-302.13 specifies remaining districts taking place from March to May 2016. By integrating that “[m]embers, including primary, secondary, and assisting members, shall randomization directly into the BWC deployment process, we were able to start their BWC recordings as soon as a call is initiated via radio or commu- conduct this study at marginally low cost to MPD. nication from OUC [Office of Unified Communications] on their mobile data To address the staggered deployment process, the data collection period computer (MDC), or at the beginning of any self-initiated police action.” varies for each police district, based on the start date of BWC deployment The general order enumerates the range of events for which officers are in that district. All outcomes were obtained at the officer level and trans- required to activate their BWCs; this list is included in . SI Appendix lated into yearly rates. These rates were calculated from the date that the Randomization was implemented using a block-randomized assignment cameras were first deployed in each district. We calculate these rates before procedure. This approach, which uses pretreatment information to group and after the intervention based on a window of 212 d, because 212 is the officers into blocks before randomly assigning a fixed number of cameras number of days between deployment and the end of the study period for to officers in each block, increases the statistical power of the experimen- the district that was the last to receive cameras. The pretreatment and post- tal design and enforces treatment-versus-control balance on the covariates treatment periods are of the same length for all districts; the pretreatment according to which blocking occurs. We applied a two-level blocking measurements come from the same 212-d window (in the previous year) as approach: The “major” blocks were the seven police districts and three the posttreatment measurements, to account for seasonality in policing and special units, and the minor blocks were constructed using a clustering algo- desensitization to the treatment over time. rithm based on the background characteristics of the officers (28). Based Because all of our outcomes are unconditional event counts translated on the eligibility requirements noted above, our sample consisted of 2,224 into yearly event rates per 1,000 offices, our measurement procedure avoids MPD members, with 1,035 members assigned to the control group and 1,189 the posttreatment bias that would be associated with measuring various members assigned to the treatment group. conditional quantities. For example, we might want to measure the frac- As anticipated in our preanalysis plan, some officers who were assigned tion of an officer’s civilian interactions that include use of force, but, since cameras did not install or use them, and some officers who were not the officer–citizen interaction is posttreatment, we cannot condition on it assigned cameras nevertheless obtained them. We estimate two compliance without the risk of bias. measures: the number of videos uploaded to the video database by treat- ment officers and the average length of the videos in minutes, as compared Estimation Strategy. We use two estimators of the average treatment with control officers. If officers complied with the randomization proto- effects: (i) difference-in-means with inverse probability weights to account col, we would expect that officers assigned BWCs would make vastly more for differential probabilities of assignment by block and (ii) regression of videos per year, as well as have a longer average length of videos, than their outcome on treatment assignment with controls for pretreatment char- counterparts in the control group. On average, treatment officers uploaded acteristics and inverse probability weights. Specifically, we control for the about 665 videos annually (compared with 14 videos uploaded among con- pretreatment value of the outcome (e.g., past use of force), pretreatment trol officers). The average video recorded by a treatment officer was over covariates for the officer, and indicators for each major block. Eq. 1 provides 11 min long, while the average video recorded by a control officer was the exact specification, as preregistered before the realization of outcomes. just 0.8 min long. For both manipulation check measures, the treatment assignment is both substantively and statistically significant (p < 0.001). We YPOST = β0 + β1Z + β2YPRE + β3Block + β4X + , [1] conclude that compliance with the study protocol was high.
Following best practices in settings encountering two-sided noncompli- where Z is the treatment indicator (officer assigned camera or not); YPRE ance, we conducted all of our analyses according to the original random is the pretreatment value of the outcome under study; Block is a vector of assignment (29). Our experiment thus recovers estimates of the effect of indicator variables for an officer’s home district or special unit; X is a vec- being assigned to a BWC on a variety of outcomes (the intention-to-treat tor of pretreatment covariates that includes race, gender, and length of effect). service; and is the error term. We estimate Eq. 1 using weighted least squares regression with inverse probability weights, which are calculated Measurement Strategy. We assessed the effect of BWCs on four families of as the inverse of the probability of each unit being in its observed condi- outcome measures: police use of force, civilian complaints, policing activity, tion (29). We use HC2 robust standard errors for variance estimation (30). and judicial outcomes. We conduct our primary analysis among officers in the seven districts of DC (n = 1,922). We exclude officers in special units from this analysis, as i) Police use of force was based on officers’ self-reported use of force (in policing activities and camera use patterns may differ between these units accordance with MPD policy). It included a count of all use of force inci- and the district officers. We conduct this analysis at the officer level, and dents as well as measures of serious uses of force (as defined by MPD report results as a yearly rate per 1,000 officers. Our analyses were con- policy), nonserious uses of force, and use of force incidents by the race ducted by two independent statistical teams, to help avoid coding errors of the subject of force. and as a check of convergence in results. ii) Civilians can file complaints in two ways: with MPD itself or with the independent Office of Police Complaints. Our measure was the total Data Availablity. The cleaned dataset sufficient for reproducing the number of complaints associated with an officer from both sources. difference-in-means estimates of the treatment effects will be made
10330 | www.pnas.org/cgi/doi/10.1073/pnas.1814773116 Yokum et al. Downloaded by guest on October 2, 2021 Downloaded by guest on October 2, 2021 ou tal. et Yokum epne ob oto fcr ny n-hr ytreatment by one-third only, officers control by were calls to from of one-third spillovers responded Approximately or officers. units, control across to effects interference treated these by but hidden outcomes, BWCs: being measured the are of the effect affect true do the cameras masking The are factors seven other that all bility in effects insignificant BWCs small, as districts. observe dis- baseline that, we police mini-experiments. in seven outcomes, seven heterogeneity note of district-to-district the also equivalent substantial sympa- of Despite the we are each conducted we We within but tricts, assigned municipalities. possibility, randomly other this were in to nation’s do the thetic in they effect no but have capital, BWCs Perhaps ways. important in to due cameras. either time the over camera, of desensitization presence the the or by to elsewhere affected diverted or being of attention interaction aware an in behavior. actually involved on civilian are effect nor no officer have the fact, neither needs Perhaps in finding find- null devices, null the The possible our explanation: is for no it obviously, explanations most possible and First few ings. a here consider We in Discussion included are null) and (all calls, behavior court Appendix. police violence on of domestic estimates and measures Effect other 41) outcomes, nonsignificant. = judicial also year, SE per were appearances, officers year, 277) estimate 1,000 per = per This (−128 SE officers effects conduct year. 1,000 disorderly The for per per zero. arrests (57 from officers, = complaints different 1,000 (SE significantly on 74 per statistically of force increase not an is of caused conduct). offi- cameras uses disorderly and that for 87) complaints, is officers) arrests guess civilian 1,000 by best force, measured Our per of (as rate use discretion estimated yearly police cer be the on a to plots BWCs (as unlikely 1 of are effect Fig. null treatment power. the statistical average reject insufficient to to no small failures detect due levels. and to these size conventional sample small, sizes, enough at large effect effect very a significance has treatment was study statistical our average Because outcomes to The measured rose result: estimate all con- null analyses on a our estimate categories, to outcome point four sistently the of each Across Results identify uniquely would data these officers. as individual esti- models, to adjusted use covariate we was that the also information mate are dataset covariate We officer-level cleaned civilians. the and the release officers to which both unable of from concerns data are privacy to raw We due the https://osf.io/p6vuh/. produced, public at make Framework to Science unable Open the at available of use and police covariates. estimator pretreatment for including (DIM) regression conduct. difference-in-means year (OLS) our disorderly least-squares both for a ordinary from arrests over findings and show officers, officers We against 1,000 filed per complaints force, groups, non-BWC and 1. Fig. hr xlnto o h ulfidnscniestepossi- the considers findings null the for explanation third A places other from different be may DC Washington, Second, vrg ifrne(ih9%cndneitra)btenBWC between interval) confidence 95% (with difference Average SI on,Dpt ao o ulcSft n utc ei oau,and Donahue, Kevin Justice Office and Executive Rashad Safety Administrator the Public City thank for Bowser, also Muriel Mayor pro- We Mayor Deputy complicated study. especially Young, new, Mayor, the a Matthew the to in Newsham, of adapted participated Peter dutifully and and who Chief Meeks, gram members Derek (ret.), sworn Fieselmann, the Lanier Heidi all Ennis, Cathy Ralph Special Chief Commander program. BWC Bromeland, to the of go impacts the thanks under- possible, to as committed have rigorously were as and not of standing, team District would research the shared our study of welcomed and Department This They Police Columbia. feedback. us. briefings Metropolitan the valuable with in without PhD, for opinions possible participated been partners and JD, who insights its Braman, individuals thoughtful and Donald many their DC and the @ thank PhD, Lab We The Doleac, from Jennifer reviewers PhD, and Egar, Bill PhD, policing many to ACKNOWLEDGMENTS. solution technological expec- such, are a our As as recalibrate We difficulties. effects. BWCs should date. of we significant that to tations statistically suggests used any experiment methodologies our detect other to infer- in unable officer of individual-level problems present several an ence avoids compar- from which our to scheme, constructed addition, randomization ability were In our exist. groups enhancing they ison large, outcomes. should a unusually judicial differences, as was and detect well size activities as sample policing complaints Our additional civilian and of force variety of uses documented large. is outcomes As unreported that on but change. effect we outcomes average of that reported true on implausible kind the effects it this small find very detect we measure however, to would speculation, unable of are matter we a unreported force, capture not of introduction do data uses the our with because going dropped However, previously BWCs. now were of that have force those of and uses be unreported, were may there it that example, case For the data. administrative with measurable not await to have experiments. will the further possibility activate that to of given evaluation are although officers cameras, may discretion of effects for level said, the incidents That on measure. depend of our 96% number on with number minimal, based the is the adherence which difference average the than in them, expect 2016 less would officer. in we was which treatment days uploaded a of videos 2% with of the associated many for service often the even (and for of Further, video call one 98% least per For at experiment. more) averaged MPD our 2016, in in nonadherence problem days that to widespread indication according a no the have activate was cameras to We fail assigned example. may for Officers their camera, variety 26). use 22, a (15, not policy for departmental may Officers, nonadherence: reasons, of of because alternative results this affect on is cameras cameras of nonpolice effect to no exposure variable. found dependent when also night, on We treatment at analysis lower. of this force effect that the of note examined use (we have we to possibility preregistered), room not this television more was explore no caption is To there effect. because closed an simply behav- margin, change and the not at do cameras, BWCs ior the Perhaps own widespread. is their (CCTV) mem- cell MPD with with civilians’ encounters bers (e.g., record regularly cameras Civilians nonpolice phones). of presence widespread postcamera versus precamera in group. either differences for outcomes no observed in and We presented affected trends before (analysis complaints deployed time cameras were civilian examined cameras and of after force we of introduction officers, uses documented the control for whether and treatment of both check officers nearby. a cameras control without As that duties their control indicates performing and calls frequently treatment were of of mix distribution a This by third officers. last the and only, officers nsmay emaue h vrg fet fBC on BWCs of effects average the measured we summary, In are that effects had have may BWCs that acknowledge We to fail may BWCs that suggested have researchers Other the by masked be may BWCs of effect true the Finally, PNAS etakKteieBre,J,PD oadGreen, Donald PhD, JD, Barnes, Katherine thank We | a 1 2019 21, May | o.116 vol. | IAppendix). SI o 21 no. | 10331
SOCIAL SCIENCES Chief Performance Officer Jennifer Reed, for dedicating their support, time, Laura and John Arnold Foundation for generous financial support. The and resources to advancing evidence-based governance and policy in the research and views expressed in this report are those of The Lab @ DC and District. Thanks to Objectively for layout and web design. We thank the do not necessarily represent the views of the foundation.
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10332 | www.pnas.org/cgi/doi/10.1073/pnas.1814773116 Yokum et al. Downloaded by guest on October 2, 2021