Maltz, Michael D.

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Journal of Criminal Law and CriminologyVolume 88Issue 4 Summer Article 12Summer 1998Which Homicides Decreased--WhyMichael D. MaltzFollow this and additional works at: https://scholarlycommons.law.northwestern.edu/jclcPart of the Criminal Law Commons, Criminology Commons, and the Criminology and CriminalJustice CommonsThis Symposium is brought to you for free and open access by Northwestern University School of Law Scholarly Commons. It has been accepted forinclusion in Journal of Criminal Law and Criminology by an authorized editor of Northwestern University School of Law Scholarly Commons.Recommended CitationMichael D. Maltz, Which Homicides Decreased--Why, 88 J. Crim. L. & Criminology 1489 (Summer 1998)0091-4169/98/8804-1489THE JOURNAL OF CRIMINAL LAW & CRIMINOLOGY VoL 88, No. 4Copyright 0 1998 by Northwestern University, School of Law Prhad in U.SA.WHICH HOMICIDES DECREASED? WHY?MICHAEL D. MALTZ*In a sense, criminologists are luckier than economists.Economists are asked to forecast what will happen to the econ-omy, and a lot of them get it wrong. Criminologists are asked toback-cast, to explain what happened after it happens, and proba-bly with about the same success as economists have at forecast-ing: even though we know what the outcome is, we often don'tknow why. But this is not for lack of trying.After reading the papers and hearing the presentations, Iam struck by the care with which the authors have analyzed thehomicide data at three levels: national, multi-jurisdictional, andsingle-city. My comments should in no way be seen as criticismsof their efforts; rather, they are suggestions as to additionalsteps that might be taken. My comments focus on two areas:disaggregation of homicide data, and considering whether "re-gression to the mean" might explain the recent decline in NewYork City homicides.I. DISAGGREGATION.As Frank Zimring pointed out in his remarks, these threepapers go from the general to the specific. The first1 discussestime trends for the whole country, the second2 focuses on eightcities, and the third3 is limited to one city. But I think that even" Professor of Criminal Justice and of Information and Decision Sciences, Uni-versity of Illinois at Chicago; Editor, Journal of Quantitative Criminology, Visiting Fellow,Bureau of Justice Statistics. The opinions expressed herein are my own and do notreflect the policies of the Bureau of Justice Statistics or the U.S. Department of Jus-tice.' Alfred Blumstein & Richard Rosenfeld, Explaining Recent Trends in U.S. HomicideRates, 88J. CraM. L. & CRIMINOLOGY 1175 (1998).2 PAMELA K. ILATIMORE ET AL., U.S. DEP'TJuSTCE, REPORT NCJ 167262, HOMIcIDEIN EIGHT U.S. CITIs: TRENDS, CONTEXT, AND POLICY IMPUCATIONS (1997).3Jeffrey Fagan et al, DecliningHomicide in New York City: A Tale of Two Trends, 88J.Cims. L. & CRnMNOLOGY 1277 (1998).1489MICHAEL D. MALTZmore disaggregation is necessary in trying to understand homi-cide trends.Homicide is a crime in and of itself; but in another sense itis the fatal outcome of a many different crimes.4 Child abuse is acrime, and when it turns fatal it becomes infanticide. Domesticabuse is a crime, and when it turns fatal it is homicide among in-timates.5 Armed robbery is a crime, and when it turns fatal it be-comes a felony homicide. I would like to see studies that lookat trends in child abuse, domestic violence, and armed robbery-as well as other offenses-and see the extent to which they are re-lated to the trends in homicide: for example, since most infanti-cides are not committed with guns, perhaps a long-termdecrease in child abuse is the cause for the long-term decreasein non-gun homicides that Fagan, Zimring, and Kim noted . Tounderstand a phenomenon, it is usually necessary to go to thenext level, to understand the context in which the phenomenonis found. Looking only at homicide statistics begs the questionof the many different motivations that may be driving the statis-tics. Knowing the authors of these papers, I am sure that theyare well aware of this, but the readers should be cautioned thatadditional steps need to be taken to provide a greater under-standing of homicide.II. REGRESSION TO THE MEAN.The three homicide studies to which I am responding8 allused homicide data from the FBI's Uniform Crime Reports(UCR) 9 and Supplementary Homicide Reports (SHR),' ° or ar-4 See generally, Richard Block & Carolyn Rebecca Block, Homicide Syndromes andVulnerability: Violence in Chicago Community Areas Over 25 Years, in 1 STUDIES ON CRIME &CRIME PREVENTION 61 (1992).' LAWRENCE A. GREENFELD ET AL, VIOLENCE BY INTIMATES, REPORT NCJ-167237,BUREAU OFJUSTICE STATISTICS, U.S. DEP'TJUSTICE (1998).6 Michael D. Maltz, Secondary Analysis of the UC" An Index of the Risk of Death Dueto Robbery, 4J. CRIM.JUSTICE 153, 153-56 (1976).7See Fagan et al., supra note 3. I doubt that this is the case, but it is exemplary ofthe type of analysis that should be done.8 See supra notes 2-4,'FEDERAL BUREAU OF INVESTIGATION, CRIME IN THE UNITED STATES, 1996. The FBIpublishes this annual report based on data sent by police departments to the FBI.1490 [Vol. 8819981 WHICH? WHY? 1491rest data from the UCR; that is, all used data that were obtainedfrom the police. It turns out that victimization data-data aboutcrime obtained from victims-can also be used to explore at leastone of the reasons given for the declining homicide rate in NewYork City, "regression to the mean.""A well-known example of this phenomenon is found in"The Connecticut Crackdown on Speeding.' 2 In 1956, follow-ing a year in which Connecticut experienced a very high rate oftraffic fatalities, then-Governor Abraham Ribicoff instituted anew policy for the State Police: zero tolerance of speeding. Thenext year there were 40 fewer traffic fatalities (a 12.3% de-crease), as shown in Figure 1, which the governor attributed tothis policy. ' -330Q320,310300290 -10280Before AfterCrackdown Crackdown(1955) (1956)Figure 1. Connecticut Traffic Fatalities, 1955-1956,0 The SHR data set can be downloaded from the National Archive of CriminalJustice Data; located at http://www.icpsr.umich.edu/nacjd, it is St-udy Number 6754.It is based on data sent by police departments to the FBI."See Fagan et al., supra note 3 at 1277." Donald T. Campbell & H. Laurence Ross, The Connecticut Crackdown on Speed-ing: Time Series Data in Quasi-Experimental Analysis, 3 L. & SoC'Y REv. 33 (1968). Thefigures from that paper have been redrawn.13 Id.1492 MICHAEL D. MALTZ [Vol. 88But it's not always that simple; a before-after comparisoncan often be very misleading. 4 When Campbell and Ross addedto the picture prior and subsequent years (Figure 2), the attri-bution of the decrease to the policy seemed much more debat-able: note that the fatalities in the first two years after thetreatment were higher than five of the six years prior to thetreatment.340320300 .280 \2602402202000 ! ! I I ! I I I'51 '52 '53 '54 '55 '56 '57 '58 '59Figure 2. Connecticut Traffic Fatalities, 1951-1959It appears that two conditions made the policy makers mis-takenly conclude that the new policy had caused the reduction.First, there was a great deal of volatility, or year-to-year variation,in the traffic fatality rate, as seen in Figure 2. This means that itwould be difficult to determine the extent to which any change(up or down) is due to the policy and the extent to which it isdue to the inherent variation in the data.Second, the policy was implemented in a year following onethat had a rather extreme number of traffic fatalities. One"4 Michael D. Maltz et al., An Artifact in Pretest-Posttest Designs: How It Can Mistak-enly Make Delinquency Programs Look Effective, in 4 EVALUATION REV. 225, 225-40 (1980);Michael D. Maltz & Stephen M. Pollock, Artiflcial Infiation of a Delinquency Rate by a Se-lection Artfact, 28 OPERATiONS RES. 547, 547-59 (1980).8WCH? WHY?would expect that, regardless of any change in policy, the nextyear's rate would be more moderate (i.e., closer to the historicalmean rate): it is harder to go up from an all-time high than it isto go down. In fact, a better name for the phenomenon mightbe "selection of the extreme," because it was the selection of anextremely high rate as the "before" year that foreordained amore moderate rate-a decrease-in the "after" year.To what extent can this phenomenon explain the New YorkCity experience? Is there evidence of volatility in the data, andis there evidence that the homicide rate in the late 80's andearly 90's was in some sense extreme?Let us first look at whether the homicide rates for New Yorkwere in some sense extreme. Evidence from a different sourceof data, the National Crime Survey (NCS), suggests that theywere." Since 1995 1 have been a Visiting Fellow at the Bureau ofJustice Statistics (BJS); one of my first projects there was to lookat the relationship between aggravated assault as reported bypolice to the FBI, and as reported by victims on the NCS, forvarious states. Although the NCS is a national survey, at thattime the sample size was sufficiently large that one could obtain16estimates of victimization rates for the eleven largest states.This permitted us to investigate the relationship between aggra-vated assault, as reported on the NCS, and homicide. Whilemost criminologists have felt that the relationship between thetwo is quite strong (because many homicides, had they not beenfatal, would have been classified as aggravated assaults), it couldnot be investigated using police-collected data because so many" Begun in 1973, the NCS was a longitudinal sample survey of 60,000 house-holds in the United States; all household members aged 12 and over are interviewedabout incidents in which they have been victims of a crime. That has been used to es-timate the nation's victimization experience. It was redesigned in 1992 and is nowknown as the National Crime Victimization Survey (NGVS). The Census Bureau col-lects the survey data for the Bureau ofJustice Statistics. Further information on thisprogram can be obtained at the BJS website, http://ojp.usdoj.gov/bjs." The Census Bureau, which collected the NCS data, provided data disaggre-gated by state, but only for the eleven most populous states (as defined by the 1990Census). Moreover, for budgetary reasons the sample size has since been reduced, sothe state-specific data available even for these eleven states may now be of more lim-ited utility.1998] 1493MICHAEL D. MALTZvictims of aggravated assault do not report them to the police.Since homicide data are considered to be very accurate and re-liable, we were able to compare two reliable data sets, NCS-collected aggravated assault data and police-collected homicidedata, for these eleven states.18 As seen in Figure 3, the relation-ship between the two is fairly strong for most states, but NewYork State's homicide rate is considerably above what one wouldexpect from the other states' data.My conclusion from using a different data set than that usedby Fagan et al is that it appears that New York State (and there-fore New York City) did have a higher than expected number ofhomicides during this period.'9 Thus we have one of the condi-tions necessary for regression to the mean-an extreme numberof homicides, considerably greater than "normal."However, another condition is necessary before one can at-tribute the finding to a statistical anomaly like regression to themean-volatility in the data so that the year-to-year variation is ofthe same order of magnitude as the presumed decrease. Fromthe data that Fagan, et al present, this is not the case.20 Homi-cide rates are consistently high for a number of years, and theyear-to-year variation does not exhibit the volatility that wouldmake it a candidate for regression to the mean.What I suggest is a friendly amendment to their paper, thatthey replace the term "regression to the mean" with "compensa-tory feedback" as a possible explanation of the increase and de-crease, in some ways equivalent to the homeostasis thatBlumstein and his colleagues noted in corrections data before" According to the NCVS, 45% of aggravated assault victimizations are not re-ported to the police. CHERYL RINGEL, BuREAu OFJUSTICE STATISTICS, REPORT No. NCJ-165812, CRINNALVICTIMIZATION 1996, at 8 (1997)."8 We chose to look at the years 1988-1990, due primarily to the availability ofNCS state-level data for those years. More recent data were not available at BJS at thetime of the study." An analysis of the SHR data, supra note 10, shows that from 1988-90 New YorkCity accounted for 84.8% of the 6202 homicides that occurred in New York State, soan extreme number in New York State is attributable for the most part to New YorkCity.20 See Fagan et al., supra note .1494 [VOL. 881998]7e+5 -6e+5-5e+5-0. 4e+5-3 Se+5-02e+5 -le+5 -WHICH? WHY?CA+. TX FL Mf OH NY IL PA NC M A NJStateNote: Homicides are multiplied by 70 to provide a meaningful comparisonFigure 3: A Comparison of NCSColiected Aggravated Assault Data with Homicide Data,for the Eleven Largest States, for the period 1988-901495-1MICHAEL D. MALTZthe 1980s.21 By "compensatory feedback" I mean that when ex-treme homicide rates began to accrue year after year, varioussteps were taken, perhaps by the police, perhaps by others, tomitigate this problem.Some observers may feel that the steps produced a "seachange" in the practices of the New York City Police Depart-ment, while others may feel that the decline was bound to occurregardless of the new police tactics, because, as Fagan et al note,similar reductions were experienced in other cities and at othertimes. On whether it was due to the police or an inevitabledownswing, the jury is still out.In a subsequent conversation with Jeffrey Fagan, he sug-gested that the rise and fall of homicides in New York City mighthave been attributable to an epidemic that grew and was sus-tained due to the combined effect of the ready availability ofdrugs and guns, and that there might have been some self-limiting aspects to the epidemic: a finite number of "suscepti-bles" that limited growth, and various factors that inhibited its"intergenerational" transmission. This explanation, too, wouldfit under the rubric of "compensatory feedback," without havingto invoke a statistical "regression to the mean" to explain thephenomenon.2' Alfred Blumstein &Jacqueline Cohen, A Theory of the Stability of Punishment, 64J. CRiM. L. & CRIMNOLOGY 198 (1973); Alfred Blumstein et al., The Dynamics of a Ho-meostatic Punishment Process, 67 J. CRIM. L. & CRIMINOLOGY 317 (1976); Alfred Blum-stein et al, On Testing the Stability of Punishment Process: A Reply, 72 J. CRIM. L. &CRIMINOLOGY 1799 (1981).22 Email conversation withJeffrey Fagan (April 13-14, 1998).1496 [Vol. 88

Which Homicides Decreased--Why

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Which Homicides Decreased--Why

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