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Understanding Crime Trends: Workshop Report (2008)

Chapter:2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld

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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
×
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
×
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
×
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Suggested Citation:"2 Factors Contributing to U.S. Crime Trends--Alfred Blumstein and Richard Rosenfeld." National Research Council. 2008. Understanding Crime Trends: Workshop Report. Washington, DC: The National Academies Press. doi: 10.17226/12472.
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2 Factors Contributing to U.S. Crime Trends Alfred Blumstein and Richard Rosenfeld Over the past 30 years, crime has become a major issue of public con- cern, of political discussion and action—often intemperate and not likely to reduce crime—and of major public expenditure. Despite its salience in the public arena, very little is known about the factors driving the crime trends, and the knowledge base is too limited to support intelligent forecasts of the direction in which crime rates are moving, especially when changing direction. Developing such a knowledge base is important for enhancing the rationality of public policies and public expenditures related to crime, particularly because many such commitments have to be made well in advance of their actual use. These include, for example, recruiting and training police forces, building prisons, and developing other interventions outside the criminal justice system. In this chapter we summarize the crime trend history over the past 35 years, examine the factors that appear to have been particularly influential in driving those trends, consider whether change in those factors could have been known in advance, and use that information to indicate some of the potential directions for enhancing the knowledge needed for better explanations and forecasts. One can expect that different crimes will be affected by different ­factors. In particular, one might anticipate that property crimes would be respon- sive to the state of economic opportunity, whereas violent crimes might be responsive to the availability of guns or to societal factors stimulating conflict. Many of these factors would be difficult to know in advance to warrant their serving as leading indicators to indicate future trends. The one factor that is often important in affecting crime is population composi- 13

14 UNDERSTANDING CRIME TRENDS tion: Different demographic groups, particularly different age and ethnic groups, display very different rates of involvement in crime. Some of these factors could be addressed in the context of generating policies intended to reduce crime. For example, to the extent that unem- ployment among teenagers and young adults is a major contributing factor to the crimes they commit, then efforts at providing job assistance, job training, or extending unemployment support for those groups could well be stimulated by their anticipated crime trends. Analysis of Some Recent Crime Trends We begin by examining trends in violent crimes, which are the most serious crimes and attract the greatest public concern. We focus on rob- bery and murder, the two violent crimes that are best measured. We devote less attention to the other two violent crimes, forcible rape and aggravated assault, both of which exhibit important measurement problems. Aggra- vated assault is troubled by the room for discretion in classifying an assault as either “aggravated” or “simple”; only if it is aggravated is it recorded as a Part I crime in the Federal Bureau of Investigation’s Uniform Crime Reports (UCR). Moreover, comparisons with the assault trends measured in the National Crime Victimization Survey (NCVS) suggest that the police have “upgraded” the recording and classification of assaults over time and classify many as aggravated that they would have treated as lesser offenses in the past (Rosenfeld, 2007a). The measurement of forcible rape is subject to important variations in whether the incident is reported to the police and counted as a Part I crime. Trends in Robbery and Murder In Figure 2-1 we compare the rates of homicide and robbery from 1972 to 2006. To provide a comparison of the two trends, we have divided the robbery rate by 25 to put robbery and murder on a comparable scale. The first observation from comparing the murder and robbery trends is their striking similarity. Both reach their peaks and their troughs within a year of each other. This may suggest that similar factors are affecting both trends, but not necessarily. It also is possible that one is driving the other. Explaining the correspondence between trends in different types of crime is an important issue for future research (see LaFree, 1998).   Except where indicated otherwise, we use the term “trends” in this chapter to refer to year- to-year variation in crime rates and associated conditions.

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 15 12 Robbery/25 10 Rate per 100k Population 8 6 Murder 4 2 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year FIGURE 2-1  Trends in murder and robbery, 1972-2006. Figure 2-1 Turning Points It is useful to examine the peaks and the troughs of these two curves as a way of identifying knowledge about the factors contributing to crime trends. The turning points are of particular interest because, once a trend has been established, the value for the current year and the current trend often yield a good prediction of the value for the next year. But the turning points are usually not easy to predict without a strong model of the factors accounting for such changes in direction. 1980 and Age Composition There was an important turning point in 1980. The rather steady rise in both rates until 1980 can be attributed to factors associated with the postwar baby boom that began with the 1947 birth cohort. As the baby boom cohorts moved into the high-crime ages of about 15 to 20, they were important contributors to the crime rise of the 1960s and 1970s. This was a consequence of there being more people in those high-crime ages and also perhaps a cohort-size effect, whereby a larger cohort in those ages stimu- lated more of its members to engage in crime (Easterlin, 1987; O’Brien, Stockard, and Isaacson, 1999). The peak cohort in the baby boom era is the 1960 cohort, which had about 4.5 million members. By 1980 that

16 UNDERSTANDING CRIME TRENDS group and large fractions of the baby boom population were moving out of the high-crime ages. Indeed, a detailed analysis of demographic effects on crime rates published in 1980, and therefore based on data for the 1970s, forecast that crime rates would peak in 1980 (Blumstein, Cohen, and Miller, 1980). Of course, that forecast was relatively easy to make because demo- graphic factors can be reliably traced well into the future, and indeed they are among the few factors that can easily be used as a leading indicator of crime rates. 1985 and the Recruitment of Young People into Crack Cocaine Markets A second turning point in robbery and murder trends took place in 1985. Crime rates declined between 1980 and 1985, the decreases associ- ated with the demographic trends already identified. There was no prior expectation that crime rates would turn up after 1985. Undoubtedly, some other factor emerged that overwhelmed the continuing demographic trend. A detailed account (Blumstein, 1995; Blumstein and Rosenfeld, 1998) highlighted the importance of the recruitment of young people into crack markets as replacements for the older sellers who were being sent to prison at a very high rate in the early 1980s. Because crack was typically sold in street markets, these young sellers had to carry guns to protect themselves against street robbers (Jacobs, 2000). They were far less restrained then their older predecessors in the use of guns, and that diminished restraint contributed to a major rise in firearm violence. The violence was augmented by the tight networking of these young people, resulting in other young people with no involvement in drug markets arming themselves for self- defense or for the status derived from carrying a gun (Fagan and Wilkinson, 1998; Sheley and Wright, 1995). Popular accounts at the time directed attention to crack as an important factor in violent crime. The street markets were located in inner-city neigh- borhoods, where violence was a norm for dispute resolution ­ (Anderson, 1999), and it arrived with widespread appeal, particularly for poor people who could not afford powder cocaine but could readily afford the low cost of crack, typically sold in small quantities. The “high” associated with crack is short-lived, 8-15 minutes, necessitating frequent purchases by regu- lar users. The high-volume street trade facilitated violence by street robbers who preyed on sellers and buyers, conflicts among sellers, and robberies by users seeking funds to purchase the drug (Jacobs, 1999). Although it was widely recognized that violence was associated with crack markets, it would have been difficult to know precisely when the turning point would occur. Crack markets began in Miami, New York, Los Angeles, and other larger coastal cities in the early 1980s, but the turning point did not occur until the major recruitment of the young replacements,

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 17 rather than with the introduction of crack. This effect is not very likely to have been anticipated in advance. 1993 and the Decline in Demand for Crack by New Users The third major turning point depicted in Figure 2-1 occurred about 1993, which was the start of the major downturn documented in The Crime Drop in America (Blumstein and Wallman, 2006; see also Zimring, 2006). That book discusses the shrinkage in crack markets that resulted from a major drop in demand for crack by new users and the consequent departure from the crack markets of the young recruits (Johnson, Golub, and Dunlap, 2006). A robust economy could absorb those young people; unemployment rates for African-American teenagers reached 20- to 30-year lows by the mid-1990s (Nasar, 1998; Nasar and Mitchell, 1999). Between 1992 and 2000, unemployment dropped by 30 percent among African Americans without a high school diploma and by over 50 percent among similarly situated Hispanics (U.S. Census Bureau, 2006). Aggressive policing focused on young people with guns probably also contributed to the violent crime drop, although the effects of such programs have been documented for only a few cities (e.g., Kennedy et al., 2001). Another contributor was the continued drop in violent crime by people over 30, resulting in part from the growing prison population ( ­ Blumstein, 2006; Rosenfeld, 2006a). During the 1990s, the median age of state ­prisoners reached the early 30s, which criminal career research sug- gests is the age with the longest residual career following a criminal justice intervention. Thus, the departure of young people from the crack markets combined with the continuing decline of violence by the over-30 population were major factors contributing to the steady decline in violent crime from about 1993 until 2000. The role of aggressive policing of young people with guns or of other innovative policing strategies introduced during the decade is less easy to identify strongly (Eck and Maguire, 2006; Rosenfeld, Fornango, and Baumer, 2005). 2000 and the End of the Crime Drop The year 2000 was not quite a turning point in the sense that it showed a trough in the crime rate, but it was certainly a turning point in convert- ing the steady decline of the 1990s to a very flat trend that continued at least until 2005. It is not surprising that the strong downward trend of the 1990s finally flattened out, but at the time it was not at all clear when that flattening would occur. The fact that the crime drop continued until 2000, resulting in low crime rates that had not been seen since the 1960s, was fortunate but not readily predictable.

18 UNDERSTANDING CRIME TRENDS The Blip in 2005 That flat trend continued over the next few years, with no changes greater than 2.5 percent. The increases continued through 2006, but in 2007 homicide and robbery rates decreased by 1.3 percent and 1.2 percent respectively (http://www.fbi.gov/ucr/cius2007/data/table_01a.html). These small changes do little to encourage a belief that neither the two previous increases nor the following decrease in 2007 represent any more than fluc- tuations around a continuing flat trend (Police Executive Research Forum, 2006, 2007; Rosenfeld, 2007b). It is easy to identify a number of factors that could be contributing to a new upward trend in violent crime, including: • reduced job opportunities for young people with minimal education, • reduced social services as a result of federal funding cuts, • reductions in the size of police forces, • diversion of police attention to terrorism issues, • slower growth in the prison population, and • diminished attention to gun control. The problem is that one could have enumerated these same factors in at least several of the preceding years or in 2007. Why they should be par- ticularly relevant in 2005 or 2006 is part of the dilemma of whether there is currently merely a blip or the start of a clear upward trend in violent crime. Trends in Burglary and Motor Vehicle Theft We have been examining just the trends in murder and robbery, the two most well-defined and well-measured violent crimes. Among property crimes, burglary and motor vehicle theft are of particular interest because of their seriousness, prevalence, and reliable measurement in the UCR. Well over half of burglaries documented in the NCVS are reported to the police, compared with only 32 percent of larcenies (http://www.albany.edu/ sourcebook/tost_3.html#3_x). Victims are even more likely to report motor vehicle thefts, partly because they depend on the police to recover their car and partly because of insurance requirements. But an important and poorly understood source of heterogeneity in motor vehicle theft is the large frac- tion of vehicles stolen for “joyriding” as opposed to economic gain. Figure 2-2 presents the time trends in burglary and motor vehicle theft rates (the latter scaled up by a factor of 2 to be comparable to burglary). We see a somewhat different pattern for burglary from that in Figure 2-1

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 19 1,800 1,600 Burglary 1,400 Rate per 100K Population 1,200 1,000 800 600 Motor Vehicle Theft 400 200 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year FIGURE 2-2  Burglary and motor vehicle theft, 1972-2006. Figure 2-2 for murder and robbery. Burglary has been on an almost steady downward trend since 1980. It is not clear why burglary, which shares with robbery the motive of economic gain, should have such a different pattern. It is pos- sible that many offenders began to substitute robbery, with its “one-stop shopping” characteristic, for burglary as the traditional fencing operations for stolen goods disappeared during the crack epidemic (Baumer et al., 1998). It is also possible that sanctions against burglary have increased faster than sanctions against robbery, thereby diminishing the difference between them and making robbery relatively more attractive as an illicit means of economic gain. The trend in motor vehicle theft, with a turning point in the early 1990s, is more similar to those for robbery and homicide than to the burglary trend, and it is consistent with qualitative accounts of stolen cars traded for drugs during the crack era (Jacobs, 1999) or for use by drug dealers to avoid having their own cars confiscated as forfeited assets. A clear need exists for research on the divergence between burglary and motor vehicle theft trends over the past 25 years.

20 UNDERSTANDING CRIME TRENDS Looking for Good Leading Indicators Although some candidate explanations are more compelling than o ­ thers, the factors underlying the recent crime trends in the United States, and especially those that might help to explain the abrupt reversals in trend we have documented, remain poorly understood (Levitt, 2004; Rosenfeld, 2004; Zimring, 2006). Given the social science community’s poor track record in explaining past crime trends, it is not surprising to find that efforts to forecast future changes are even less promising. Reliable forecasting requires either strong time-series predictors or knowledge of leading indi- cators that can be used to predict future changes in crime rates, such that knowledge of the indicator’s value at t0 yields an accurate prediction of the change in crime at t1, some later time. We consider the forecasting possibili- ties of several of the factors already mentioned and a few additional ones that appear to hold some promise at both the national and local levels. Demographic Trends As noted previously, demography provides one of the best leading indicators. On one hand, it is well established, and it can be forecast well into the future. It invokes the information contained in the well-known age-crime curves and in racial and ethnic differences in victimization and offending patterns. When there are no other comparably strong influences, demographic changes may provide the best prediction of future crime trends. On the other hand, we also have mentioned in earlier sections other impor- tant factors that can dominate the demographic effects. This is particularly true when the demographic changes are relatively slow. Indeed, during the sharp crime drop of the 1990s, age composition changes were trending in the wrong direction: the number of 18-year-olds in the U.S. population was increasing while crime rates were declining for other reasons. Age Composition The role of age composition can be assessed from Figure 2-3, which shows the number of people of each age in 2005. The strong effect of the baby boom is seen in the right-hand portion of the curve. There was a 30 per- cent increase in cohort size between 1945 and 1947 (the two cohorts were 60 and 58 years old, respectively, in 2005). Subsequent cohorts were increasing in size until the peak 1960 cohort (which was 45 years old in 2005). Look- ing at the cohorts between ages 0 and 20 one does not see any important changes in cohort sizes, with most of those cohorts varying around 4 million persons per cohort. Thus, changing age composition is not likely to provide a substantial influence on crime rates for the next 20 years.

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 21 5 4 Number at Each Age 3 (Millions) 2 1 0 0 10 20 30 40 50 60 70 Age FIGURE 2-3  Demography: Age distribution of the U.S. population in 2005. Race and Ethnicity Figure 2-3, editable Because there are sizable differences in crime involvement among racial and ethnic groups, changes in their size might be important in affect- ing crime trends. We can assess the probable race-ethnic effects with the data in Table 2-1, which presents projected changes in the composition of the U.S. population by race and ethnicity in five-year intervals through age 25 (based on data in http://www.census.gov/ipc/www/usinterimproj/ usproj2000-2050.xls). The table shows that the growth rate in the white and black populations is generally quite slow (less than 1 percent per year for almost all age-year combinations), while the growth in the Hispanic population is somewhat greater (typically on the order of 1-2 percent per year). These aggregate growth rates are generally quite small and so are not likely to have a major effect on crime rates during a period of major change, such as the 1990s, when the homicide and robbery rates fell by about 5 percent per year, or between 1985 and 1991, when they rose by 3 to 4 percent per year. It is possible, of course, that during more limited periods or for particu- lar ages the demographic shifts could become important. Table 2-2 presents the projected trends for 15-year-olds as an illustration of that effect. We note that during the 2000-2005 period, both blacks (2.9 percent) and His-

22 UNDERSTANDING CRIME TRENDS TABLE 2-1  Annual Percentage Change in U.S. White, Hispanic, and Black Populations by Age Over Five-Year Intervals, 2000-2020 Age White Hispanic Black 5 0.1 1.9 0.64 10 –0.6 1.9 –0.02 15 –0.6 2.5 0.36 20 –0.6 1.6 0.09 TABLE 2-2  Annual Percentage Change in U.S. White, Hispanic, and Black 15-Year-Olds Over Five-Year Intervals, 2000-2020 Years White Hispanic Black 2000-2005 0.5 4.5 2.9 2005-2010 –2.2 1.6 –2.1 2010-2015 –1.0 1.5 –1.2 2015-2020 0.5 2.4 1.7 panics (4.5 percent) had appreciably larger annual growth than over the entire 20-year period. This might well have introduced a demographic effect into the crime changes in recent years, as the 15-year-olds move toward the peak ages of the age-crime curve. But the rate of change for the later years is smaller for Hispanics and negative for blacks, so it is likely that any such demographic effect would be short and transient. Incarceration Another factor with some promise as a leading indicator for crime is the extent of incarceration. There is little question that incarceration at the l ­evels used in the United States has a crime reduction effect, most specifi- cally through incapacitation. But that effect varies with crime type, and it is quite dubious for offenders engaged in illicit markets, like drug dealers, in which replacements can be recruited when offenders are sent to prison (Blumstein, 1993, 1995). Also, the effect will differ with the offender’s age (e.g., those in their 30s have the longest residual career length) and with the length of the sentence being served. Some policy analysts argue that incarceration is the dominant influence on crime, with the growth of incar- ceration during the 1990s crime drop given as a dramatic case in point. But incarceration was also increasing during the 1980s, when crime rates were going up. This highlights the fact that crime rates are affected by a

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 23 multiplicity of factors—some pushing them up and others pushing them down—and at any time one or another could be dominating the rest. It is the net sum of these factors that results in a net positive or negative effect on crime rates. Such considerations call for multivariate investigations of the impact of incarceration on crime rates. That research has, with exceptions, shown that crime rates decline with increases in incarceration, net of other influences (Levitt, 1996; Marvell and Moody, 1994; but see DeFina and Arvanites, 2002). Rosenfeld and Fornango (2007) estimate that rising incarceration rates accounted for about 19 percent of the decline in national robbery rates and 23 percent of the drop in burglary rates during the 1990s, controlling for the effects of economic conditions, growth in police per capita, changes in age and race composition, and lagged crime rates. These results are similar to those reported by Spelman (2006), Rosenfeld (2006a), and Levitt (2004). This convergence in results does not guarantee a similar effect under any other circumstances, but it does highlight the ability to make reason- able estimates of the effects of incarceration on recent U.S. crime trends. Using the elasticity estimates that derive from these analyses and the time lag between observed increases in imprisonment and crime reductions (gen- erally estimated as one year but sometimes longer), one should be able to anticipate future effects on crime as incarceration rates and related policies change. For example, given the recent decline in the net growth of incar- ceration, the large numbers of individuals being released from prison (about 700,000 per year), and potential difficulties in readjusting to civilian life, one might have expected some reduction of the incarceration effect on r ­ obbery and homicide over the past few years. Future research, however, should consider two limits on the relation- ship between incarceration and crime. First, if the crime reduction effects of incarceration are assumed to operate mainly through incapacitation, they are likely to be strongly age-graded. The crime rates of younger people, who have a comparatively low risk of incarceration, should not be affected as much as those of adults by aggregate changes in the incarceration rate, which largely reflects the incapacitation of offenders in their late 20s and 30s (again, the median age of prisoners is early 30s). A second condition limiting the crime reduction effects of imprison- ment concerns the diminishing effect of incapacitation as imprisonment rates increase. Research indicates that the effect of imprisonment on crime varies with the scale of incarceration. The crime reduction effects of impris- onment grow larger as incarceration rates increase and then level off and could well diminish (Canela-Cacho, Blumstein, and Cohen, 1997). There is some indication that additional expansion in incarceration may actually be associated with crime increases (Clear et al., 2003; Liedka, Piehl, and Useem, 2006).

24 UNDERSTANDING CRIME TRENDS If replicated, these findings can help to reconcile rival theoretical claims about the impact of incarceration on crime. Some analysts point to the disruptive effects of high incarceration rates on family functioning and community organization, maintaining that under such conditions incar- ceration increases crime (Rose and Clear, 1998). Others argue that the incapacitation effects of incarceration must diminish with the incarceration of less serious offenders inherent in prison expansion (Spelman, 2006). And others cite the now substantial econometric literature on imprisonment as evidence for the deterrent and incapacitation effects of incarceration on crime (Levitt, 2002). All may be correct. There is a clear need for research on the impact of incarceration on age-specific crime rates as the scale of imprisonment changes. The Economy The idea that crime rates rise and fall with economic conditions has a long pedigree in criminology. Early studies sought to connect crime rates to the changing prices of staple commodities, such as wheat or rye (Cook and Zarkin, 1985, p. 118). More recent research has generally used the unemployment rate to measure economic performance. Employment opportunities represent an important means of diverting people from need- based criminal activity. This is especially the case with teenagers, for whom employment represents the natural role transition to adult status. Although many studies have attempted to link unemployment rates with crime, the results have been strikingly diffuse: some find a positive association, some find a negative association, and many find not much of an association at all (Kleck and Chiricos, 2002). These disparate results can be attributed, in part, to the meaning of “unemployment rate.” On one hand, for example, the unemployment rate may have been high in Silicon Valley following the “dot-com” bust, but the newly unemployed people were not likely to turn to crime—or, at any rate, the types of crime counted in the FBI’s Part I crimes. On the other hand, employment opportunities for teenagers can have a powerful influence on whether they begin or continue to engage in crime (Freeman, 1996). Changes in the aggregate unemployment rate are likely to be a very blunt instrument for identifying the effects of economic conditions on crime trends. Changes in age-, race-, and sex-specific unemployment should yield better estimates of the criminal involvement of groups that have a dispro- portionate influence on crime trends at both the national and local levels. Other economic indicators have shown some promise in explaining aggregate and age-specific crime trends, including wages (Grogger, 2006) and state-level gross domestic product (GDP) (Arvanites and DeFina, 2006). However, the forecasting potential of such indicators is limited because

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 25 they are generally estimated as coincident and not leading indicators of crime changes, and they are themselves difficult to anticipate. It would be extremely desirable to find macroeconomic indicators that can serve as leading indicators of crime rates. One possible candidate is consumer sentiment. Aggregate consumer expectations derived from monthly population surveys may outperform formal economic models and the forecasts of professional economists in predicting future unemployment and inflation trends (Curtin, 2002, 2003). They also have proven to be relatively accurate predictors of subsequent changes in real GDP (Golinelli and Parigi, 2004). The Index of Consumer Expectations, taken from the University of Michigan’s monthly consumer surveys, is included in the Leading Indicator Composite Index published by the Bureau of Economic Analysis of the U.S. Department of Commerce. Perhaps the most salient advantage of the consumer surveys over the standard measures of economic conditions is that they measure the sub- jective experience of economic hardship and change. Individuals may, of course, misjudge the timing or significance of various economic conditions, but they are likely to be more reliable guides to their own perceptions of economic conditions than researchers who must rely on more or less informed assumptions about those perceptions. Recent research has revealed sizable and robust effects of a summary measure of consumer sentiment on trends in U.S. robbery and property crime rates (Rosenfeld and Fornango, 2007). Year-over-year increases since 1970 in consumer confidence and optimism are associated with year-over- year reductions in robbery, burglary, larceny, and motor vehicle theft rates. These effects withstand controls for age and race composition, imprison- ment rates, police per capita, lagged crime rates, and the possible reciprocal influence of crime on public economic perceptions. They are largely inde- pendent of the effects of unemployment and real GDP per capita. Perhaps most importantly, consumer sentiment leads (by one year) and is not simply a contemporaneous indicator of robbery and property crime changes. If these results are replicated in future research, they hold some promise for perceptual measures of economic conditions as leading indicators of crime rate changes. The findings to date on the impact of the public’s economic percep- tions on crime rates are limited to property crimes and the violent crime of robbery. In light of the similarity between the homicide and robbery trends shown in Figure 2-1, one might anticipate a similar relationship to homi- cide. An initial indication is the correspondence between homicide rates and the Index of Consumer Sentiment over the past 45 years, as shown in Figure 2-4. To better reveal the correspondence between the two series, the consumer sentiment measure has been inverted so that low values reveal consumer confidence and optimism. Both series have been regressed on a

26 UNDERSTANDING CRIME TRENDS 2.5 Consumer Sentiment 2.0 Homicide 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 FIGURE 2-4  Detrended index of consumer sentiment (inverted) and U.S. homicide rate, 1960-2005. Figure 2-4 linear counter to highlight year-to-year deviations from their respective time trends. The two series move in strikingly similar patterns, reaching peaks and troughs at about the same time, including the important turning points during the 1980s and 1990s discussed earlier. Public economic perceptions certainly warrant attention in future research on changes in both property and violent crime rates. Other Proposed Factors Aside from the previous enumeration, a number of other explanations have been proposed in the literature. The one that has probably received the most currency, perhaps because of the creativity of the suggestion and also because of its elaboration in the bestselling book, Freakonomics (Levitt and Dubner, 2005), is that of Donohue and Levitt (2001). This analysis appears to show that the legalization of abortion in 1973 as a result of the Roe v. Wade Supreme Court decision resulted in fewer unwanted births and hence reduced the criminality of subsequent birth cohorts. Their original analysis suggested that at least half of the crime drop of the 1990s was thus attribut- able to the legalization of abortion, although in a subsequent analysis they dropped that factor to one-quarter (Donohue and Levitt, 2004).

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 27 There has been considerable challenge to the Donohue-Levitt con- clusion. Joyce (2004) challenged the salience of abortion by showing no significant drop in fertility, suggesting that the legalization could well have been matched by illegal abortions prior to 1973. Comparing crime rates of similar cohorts born before and after legalization, he found only period effects. His various analyses conclude with a strong and consistent finding of no appreciable effect of abortion on crime rates. Zimring (2006) argues that if there were a profound effect of abortion legalization on unwanted births resulting in a major crime decline, one should see that effect replicated in school performance, labor force partici- pation, and many other facets of the enhanced socialization of the post-Roe cohorts. He suggests that finding it only with respect to crime is an artifact of the shortcomings of the analysis rather than the hypothesized abortion effect. He also points out that the liberalization of abortion policy in other nations evidently has not produced corresponding reductions in crime. These criticisms imply that the Donohue-Levitt analysis omits impor- tant factors other than abortion policy changes that have influenced crime trends. A critical omission is any consideration of the influence of the changes in the crack market and its participants in the late 1980s and early 1990s. A key part of the Donahue-Levitt argument hinges on the different effects in five states—importantly including New York and California—that legalized abortion before 1973. As demonstrated by Cork (1999), these two states’ largest cities, New York and Los Angeles, were early initiators of the crack epidemic and that could have accounted for the early start of the crime drop in those two states. Thus, it seems reasonable to conclude that, while among the many factors affecting crime rates there may well have been some limited effect of abortion and the consequent reduction in unwanted children, the important omitted variables in the initial analysis and the replications showing no significant effect suggest that any such effect is likely to be quite small. Similarly, studies by Reyes (2007) and Nevin (2000) comment on children’s exposure to lead and its effect on intelligence and on violence. This research builds on early work by Needleman (1995) on the effects of children’s exposure to lead on their intelligence measured by IQ scores. Lead was introduced into gasoline in the early 1940s, reached a peak in the early 1970s as environmental controls were introduced, and declined thereafter. There is a clear similarity between time trends in environmental lead levels and violent crime rates lagged by 23 years. But demographic trends—the arrival and waning of the baby boom generation from the high- crime ages—coincided roughly with the arrival and departure of leaded gasoline, and so the apparent effect of exposure to lead on crime rates may be confounded with demographic change.

28 UNDERSTANDING CRIME TRENDS 160 140 Atlanta 120 Number of Murders Indianapolis 100 Kansas City St. Louis 80 Las Vegas 60 Memphis Milwaukee 40 Oakland 20 0 2000 2001 2002 2003 2004 2005 Year FIGURE 2-5  Number of murders in eight cities over six years. Figure 2-5 LOCAL VARIATION IN CRIME TRENDS The general consistency across cities of the large crime drop during the 1990s could leave the impression that crime trends are reasonably uniform across cities. In fact, crime trends are much more likely to vary across ­cities, and that has been very much the case since 2000, when the aggregate national trend has been flat. This is reflected in Figure 2-5, which depicts recent pat- terns across eight cities, each of which had about 100 homicides per year. This graph clearly highlights the diverse patterns of change across cities, although most of them turned up in 2005. This suggests that, at least until 2005, the recent crime trends have been driven more by local conditions than by any general national demographic, incarceration, or economic trend. Nor were the crime increases recorded in 2005 and 2006 uniform across cities. Figure 2-6 displays changes in robberies in 28 cities between 2004 and 2006. On average, robberies in the 28 ­cities increased 2.9 per- cent over the two years, and several cities registered declines. An average yearly robbery increase of 1.5 percent, as well as a decrease or an increase of less than 10 percent over two years for almost two-thirds of the cities, do not constitute the “gathering storm” of violence chronicled in a recent influential report based on a different sample of cities (Police Executive Research Forum, 2006, 2007).   he T full-year 2006 data were drawn from the police department websites of the 28 cities at about the time that the preliminary six-month results were reported by the UCR.

Richmond Indianapolis Hartford Dallas Atlanta New York Cincinnati Portland Chicago Fort Worth Los Angeles Oklahoma City Net Change = 2.9% Tulsa Jacksonville Fresno Median = 3.8% Seattle San Antonio Houston Greensboro Phoenix Tucson Charlotte St. Louis Washington San Diego Arlington Minneapolis Virginia Beach –30 –25 –20 –15 –10 –5 0 5 10 15 20 25 30 35 40 45 FIGURE 2-6  Percentage change in robberies in 28 cities, 2004-2006. 29 Figure 2-6, landscape

30 UNDERSTANDING CRIME TRENDS The natural place to turn for identifying local factors affecting crime rates is the rich body of criminological theory and research, including lon- gitudinal investigations of factors affecting the development of criminality, and evaluation research on local crime-control initiatives. Some of these factors may be distinctively local, such as particular policing tactics; some may be regional, such as the progression of a particular drug market; and some may be national, such as the result of a change in federal public assistance policies. Of course, such factors may be as difficult to forecast as crime rates themselves. Furthermore, the existing research generally does not link specific factors affecting individual criminality (e.g., parent- ing styles or temperament) or specific local interventions (e.g., hot spots policing) to broader changes in crime rates, so one knows very little about the probable effects of such conditions and programs on crime trends were they brought to scale (Rosenfeld, 2006b; Wilson, 2002). We now consider factors that are relevant at the local level: policing strategies, tactics, and management; firearm availability; drug markets; the presence of local gangs or other oppositional groups; and variation in socialization and the availability of social services. Policing A recent review concluded that the many and diverse changes in p ­ olicing strategies and tactics in the United States during the 1990s prob- ably contributed little to the national crime drop (Eck and Maguire, 2006). But that conclusion is as much a reflection of the sparseness and quality of the underlying research as of the effectiveness of the policing innovations (Rosenfeld, Fornango, and Baumer, 2005). For example, we are aware of only four investigations of the effects on precinct-level violent crime trends of New York City’s widely emulated program of increasing arrests for minor quality-of-life offenses. Two of these studies concluded that the quality-of-life initiative had statistically significant but small effects on New York’s violent crime decline during the 1990s (Messner et al., 2007; Rosenfeld, Fornango, and Rengifo, 2007); one concluded it had no effect (Harcourt and Ludwig, 2006); and the other maintained that the initiative was responsible for all of New York’s violent crime drop (Kelling and Sousa, 2001). Until the disparate results of these investigations are reconciled in future research, the effects of quality-of-life policing on rates of serious crime in New York—and the many other cities where similar strategies have been instituted—will remain an open question and a very contentious policy issue. The innovation that has received the most consistent research support is so-called hot spots policing. This strategy concentrates police resources in areas of elevated criminal activity identified on the basis of continuous

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 31 monitoring of crime reports. Hot spots policing has been shown to reduce localized crime without displacement to other areas (Braga, 2005). But it is not known what effect such programs have, net of other influences, on the crime trends in the cities where they have been implemented. Firearms Firearms are phenomenally ubiquitous in the United States. There are perhaps 75 million handguns in civilian hands. In the great majority of cases, these guns belong to generally law-abiding individuals who pose no threat of using their guns in criminal activity. But this ubiquity also ensures that many guns will find their way into the hands of people, especially young people, who acquire them illegally, who are much more likely to use them with much less restraint, and who are likely to use them in a criminal way, either for interpersonal violence or as a weapon for robbery. Various policing efforts are targeted at suppressing illicit gun traffick- ing or at confiscating guns from inappropriate carriers. Reports of “shots fired” provide a key indicator of the presence of guns and their likely misuse, and so warrant police efforts to interdict such activities. Recent evidence suggests that shots-fired calls may serve as a reliable leading indi- cator for short-term forecasts of more serious offenses (Cohen, Gorr, and O ­ lligschlaeger, 2007). A relationship between firearm possession and firearm homicide rates in local areas has been documented (Cook and Ludwig, 2006; Hemenway, 2004; National Research Council, 2005). The causal direction of this rela- tionship remains in dispute, however, with some researchers maintaining that firearm violence elevates rates of gun ownership, but not the reverse (Kleck, 1997). A recent study using instrumental-variable methods found a mutually reinforcing relationship between firearm ownership and firearm homicide rates for a nationally representative sample of metropolitan and nonmetropolitan counties (Rosenfeld, Baumer, and Messner, 2007; see also Cook and Ludwig, 2006). Firearm ownership increased rates of firearm homicide, and they, in turn, increased ownership. Additional research on the relationship between trends in firearm possession and firearm violence in the United States is clearly needed, especially research on the acquisi- tion of firearms by persons at high risk for criminal violence (see National Research Council, 2005). Drug Markets As indicated earlier, drug markets can be an important source of vio- lent crime. They generate violence because disputes between buyers and sellers or between competing sellers cannot be settled through recourse to

32 UNDERSTANDING CRIME TRENDS the police, courts, or other formal means of conflict resolution. They also generate property crime and robbery resulting from many drug users being unable to maintain jobs, or, even if they do work, being unable to gener- ate the income needed to support their addiction and turning to crime to provide the money to buy drugs. It is also the case that drug markets vary considerably in the degree to which they stimulate violent or property crimes. It is rare, for example, for marijuana markets to generate much violent crime. But crack street markets have been strongly involved in both violent and property crimes. Typically, a new drug does not show itself in all places at the same time but rather takes hold in some places, often in the largest cities on the coasts, and spreads over time to other places. That pattern then provides an early warning of its diffusion. In some cases the diffusion will be very rapid, as was the case with crack and the firearm violence associated with it (Cork, 1999; Messner et al., 2005). The drug getting the most attention in recent years is methamphetamine, which started in the West several years ago and has been slowly working its way east, still not much further than the Midwest. Abundant anecdotal evidence, mainly from law enforcement agencies, suggests that methamphetamine stimulates violent crime in small towns and rural areas, but systematic research is lacking on the relationship between methamphetamine and criminal violence. One important source of information on the local features of drug use is the program managed by the National Institute of Justice (NIJ) initially entitled Drug Use Forecasting (DUF) and later changed to Arrestee Drug Abuse Monitoring (ADAM). In this program, booked arrestees in cities across the country were interviewed and given urine tests quarterly to assess the prevalence of illicit drugs and to identify the drugs being used by this population. This program provided valuable information to local commu- nities on the time trends of drug abuse and the nature of the drugs being used. Collectively, it also provided a corresponding national picture of the time trends in drug abuse. The program was canceled by NIJ because of a shortage of funds, even though those funds were minuscule compared with the national effort at drug control. Gangs and Other Special Groups There will always be certain population subgoups that are disaffected from or actively hostile to their social environment. In Code of the Street, Elijah Anderson (1999) describes a small segment of the inner-city poor as “street people” who live among much larger numbers of “decent people.” The street people see little prospect for their future, have a very low thresh- old of insult, and are prepared to use even extreme violence to avenge per- ceived disrespect. The violence often involves groups, and sometimes more

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 33 formal gangs, and exhibits processes of retaliation that can escalate into a sequence of assaults. Indeed, when they see a significant jump in criminal violence within a city, local officials and criminologists often link that jump to the actions of such groups. It is difficult to know in advance when such escalation will occur or the extent to which retaliatory violence spirals are themselves a consequence of changing economic conditions, incarceration levels, drug market conflicts, police actions, or other factors. More formal street gangs engage in similar kinds of retaliatory activity with each other. American street gangs and the peer groupings Anderson (1999) describes probably differ more in degree than in kind. Los Angeles and Chicago are notorious for the long-term operation of gangs with formal names, hierarchical structures, and formal signs and colors, but most street gangs are loosely organized, fragmented groups with fleeting membership (Klein, 1995). The number of street gangs and gang members increased during the 1980s and early 1990s, in tandem with the national rise in youth homicide, fell through the end of the decade, and has flattened in recent years—not unlike the pattern for youth violence generally (Egley and Ritz, 2006). This correspondence between the rise and decline of street gangs and street crime implies that gangs might have been an important cause of the broader crime trends. Although entirely plausible, it is just as likely that gangs formed in response to the rising tide of violence and diminished in number as the violence decreased. The causal relationship between the trends in gangs and violent crime is probably reciprocal, a hypothesis supported by two well-established facts about why adolescents join gangs and the consequences of member- ship for individual offending and victimization. An important motive for joining is protection from violence in the local community (Decker and van W ­ inkle, 1996; Klein, 1995). Once in the gang, however, adolescents’ crimi- nal offending and victimization increase, and when they leave the gang, their offending and victimization levels fall (Peterson, Taylor, and Esbensen, 2004; Thornberry et al., 2003). Gangs may therefore arise as youths seek protection from escalating violence, and as they proliferate their internal dynamics may generate further increases in violence. When the level of violence begins to drop, gangs stop forming or break up, which hastens the decline in violence. Testing these hypotheses with aggregate-level data on gang and violence trends is an important topic for future research. Socialization and Social Services The propensity for young people to be involved in crime is affected by the socialization processes they experience from birth through adolescence. Family disruption, family size, and parental supervision, conflict, and crimi-

34 UNDERSTANDING CRIME TRENDS nality are all important determinants of individual delinquency and crimi- nality. Family-based crime prevention programs have been shown to reduce children’s antisocial behavior and arrests during adolescence. The family factors affecting delinquency and crime may be modifiable by investments in a wide array of social services, but especially in pre- and postnatal home visits and parent training programs, which demonstration projects have shown to be especially effective (Farrington, 2002). The availability of such services, even when supported by local funding, is particularly sensitive to federal social welfare investments. As federal budget deficits have grown in recent years, such services have been cut back and become more depen- dent on local financing, which has been under considerable strain in many urban areas, where such support is most needed. The same is true of more narrowly focused violence prevention programs, including those of proven effectiveness, such as the Blueprints program evaluated by the ­Center for the Study and Prevention of Violence at the University of Colorado (http:// www.colorado.edu/cspv/blueprints/index.html). A challenging research need is to link individual-level data on child- hood socialization to aggregate trends in social welfare investments, and both of these to crime trends. It should be possible in principle to integrate data from longitudinal studies of child and adolescent development with aggregate budgetary and crime data for those cities in which the longitu- dinal developmental studies have been conducted over an extended period (e.g., Pittsburgh, Rochester, Denver, Montreal). Until such multilevel studies are undertaken, one will not know to what extent the risk factors identi- fied in developmental research can serve as leading indicators of changes in crime rates or to what degree public investments in social services can help to ameliorate childhood risks for delinquency and crime. Future research needs We have identified several factors that prior research suggests have been associated with changes in crime rates in the United States over the past several decades. These include demographic shifts, growth in incarceration, drug markets, and changing economic conditions. We have discussed other factors, such as policing innovations, firearm availability, street gangs, childhood socialization, and investments in social services that may influ- ence crime trends but for which the existing evidence is too fragmentary to develop accurate effect measures. Much remains to be learned about the factors affecting crime trends, including those we already know something about. For example, the crack markets were implicated in the rise of youth fire- arm violence during the late 1980s, and an important reason was because young people replaced the adult drug sellers who were sent to prison

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 35 (Blumstein, 1995). That interpretation is consistent not only with the rising imprisonment rates for adult drug dealers during the 1980s but with the ris- ing rates of drug arrests and gun violence among minority adolescents that occurred after 1985. The evidence for this explanation could be augmented by results from panel studies showing that the largest increases in youth firearm violence were concentrated in those cities with the largest increases in drug arrests of crack dealers. Those increases, in turn, should have hap- pened in those cities displaying the largest increases in the incarceration of adult drug sellers. Such evidence would further support a leading explana- tion of the upturn in violent crime during the 1980s that has important policy implications: an unanticipated negative consequence of the intensive sentencing policies initiated as part of the war on drugs was its contribution to the rise in youth violence. To take another example, we have argued that the strong economy of the 1990s contributed to the decline in violence. During the longest peace- time economic boom on record, tight labor markets were able to absorb minority youth who no longer could make money in the shrinking drug markets. The implication is that the economic expansion conditioned the effect on crime of the drop in demand for crack. In the absence of legitimate employment opportunities, more young people would have pursued other illegitimate opportunities for making money. Again, this story is compatible with several co-occurring trends at the national level in the 1990s, including falling unemployment rates among minority youth and declining demand for crack (Golub and Johnson, 1994). Stronger evidence, with direct rel- evance for employment policies, would come from studies showing that the impact of declining drug markets on crime reduction was strongest in those cities exhibiting the sharpest increases in minority youth employment and earnings. The Future of Crime Forecasting Developing sound empirical explanations of past crime trends is an important means of improving the capacity to make informative and reason- ably accurate forecasts of future changes. As approaches are developed to estimating and forecasting the factors contributing to crime trends, it is useful to recognize that there are few significant social or even natural phenomena for which there are good forecasts. For example, a leading group of weather forecasters inaccurately predicted a “very active” 2007 hurricane season. The group’s forecast for 2006 overpredicted hurricanes; the year before that, when Hurricane Katrina hit, they erred on the low side. Forecasts of when and where emerging tropical storms will land tend not to be very accurate (Merzer, 2007; see National Research Council, 2006, for a useful discussion of incorporating uncertainty into the dissemination of weather forecasts).

36 UNDERSTANDING CRIME TRENDS The field of macroeconomics offers another example of considerable effort to develop forecasting models and abundant forecasting failures (Gross, 2007). Despite the large industry devoted to economic forecasts, one week saw the current and former chairmen of the Federal Reserve come out at the same time with strongly differing forecasts, one suggesting the possibility of a recession within the year and the other commenting on the current strength of the economy. Given the resources available and the experience they both bring, and given that the forecast extended for only one year, it is humbling—but also encouraging—to enter the challenge of forecasting crime. The encouragement comes not from the accuracy of weather or eco- nomic forecasts but from the seriousness of the efforts, stimulated no doubt by the strong economic interest in their forecasts. Criminologists are noto- rious for the inaccuracy of their crime forecasts; consider only the widely publicized prediction of a crime boom brought on by marauding “super predators” (Dilulio, 1995) issued just as crime rates began their historic plunge in the 1990s. The problem with such forecasts is not simply that they are wrong, but also that they are based on minimal systematic analysis. One therefore learns nothing from them. When meteorologists or econo- mists fail to accurately predict the next tropical storm or recession, they can acquire new knowledge about the conditions affecting the weather or economy, which can be used to enhance the data and refine the models used in making the forecasts. Opportunities for such self-correction are absent when forecasts are created in the interest of advocacy, with no opportunities for challenge and replication. Only with a large investment of resources can criminologists hope for their forecasting models to become as meaningful as those from economists, let alone meteorologists. National and Regional Estimates It is useful to differentiate efforts at generating national estimates, regional estimates, and local estimates for a particular city or neighborhood. For the national estimates, it is difficult at this point to identify any reliable leading indicators other than demographic shifts. Nevertheless, efforts to identify such indicators are desirable, at least in part because such forecasts could influence the level of federal financial support for policing and other local criminal justice initiatives. A measure of collective economic percep- tions from consumer surveys seems to be a strong contemporary correlate of changes in several crime types and may well be a leading indicator of some (Rosenfeld and Fornango, 2007). Similar considerations would apply in the search for multistate regional indicators. There are good reasons to believe that reliable regional indicators might be found because regions are generally more homogeneous than the nation as a whole. The consumer

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 37 sentiment data are available for the four major census regions. For both the nation and regions, one would also look to drug activity, particularly drugs that are sold in street markets or that start a rapid escalation of demand, as primary indicators of rising crime rates ahead. Local-Level Estimates Both economic and drug market indicators should also be evaluated for their contributions to crime forecasts at the neighborhood or city level. Local efforts could be more effectively targeted than national resources or policies, and so developing better estimates for local application would be particularly desirable. The consumer sentiment data are not available for cities or metropolitan areas, but the crime-forecasting capabilities of other economic indicators of local conditions, such as youth unemployment and wage rates, should be investigated. A useful research task would be to use traditional regression-based clustering models to aggregate a large number of cities into subgroups that display similar patterns in crime trends. Alter- natively, one might use trajectory analysis (Nagin, 2005) to aggregate into groups cities that have displayed similar crime trends. One could then look for leading indicators of the patterns for each of these trajectory groups. Because the different trajectory groups will have different patterns, there is a strong likelihood that different factors affect them. We anticipate that in the contemporary environment, drug markets, incarceration levels, and employment opportunities for unskilled young men are likely to be impor- tant factors affecting crime trends in the larger cities. Whether the same factors also help to explain the trends in smaller cities is a research ques- tion for which regression analysis, including interactions with city size, or trajectory analysis could well contribute. At the neighborhood level, crime, especially violent crime, is concen- trated in relatively few areas of the city, a pattern similar to the highly skewed distribution of serious offending across individuals (Chaiken and Chaiken, 1982). Researchers have begun to use trajectory methods at the neighbor- hood and even smaller levels of aggregation with some promising initial results (Griffiths and Chavez, 2004; Weisburd et al., 2004). Forecasting at this level poses special research challenges but also some distinctive oppor- tunities for acquiring information from individuals familiar with the local environment. Police, youth workers, social service providers, and neighbor- hood residents are often sensitive to changes in mood and activity patterns and signs of disorder that can serve as early warnings of an upturn in crime. Short-term forecasts of crime patterns at the neighborhood level, such as those recently produced for the Pittsburgh Police Department (Cohen, Gorr, and Olligschlaeger, 2007), also are likely to be of more immediate interest to police managers than forecasts of crime rates for the entire city.

38 UNDERSTANDING CRIME TRENDS An exciting potential for forecasting at the local level lies in the rich individual and family data from long-standing longitudinal investigations of delinquent and antisocial behavior that are situated in several cities. The challenge is to evaluate the indicators that provide good predictions, some- times years ahead, of individual criminal involvement for their potential as leading indicators of neighborhood or city crime trends. This will require multilevel analyses that go beyond the now common practice of assessing “neighborhood effects” on individual criminal behavior by estimating the effects of aggregated individual propensities on community crime rates. Such research will necessitate bringing together researchers with quite different interests and skills into collaborative projects. The science of crime forecasting could be advanced significantly by incorporating findings from longitudinal research on individual criminal behavior into analyses of changes in crime rates over time. Building the Research Infrastructure The relevance of these proposals for future research on crime trends to assessments of crime control policy will be limited in the absence of a substantial upgrading in the nation’s capacity to monitor crime trends. We have already observed the divergent interpretations following reports of some recent crime increases, which stem in large part from the time delay between the availability of local crime data and the UCR’s dissemination of aggregate crime statistics. Such delays can provide an opportunity for advocacy groups to leap into the information breach with data of uncertain reliability. There is no technical reason why the recording and dissemina- tion of crime data cannot be as rapid as, say, the compilation and online dissemination of unemployment data by the Bureau of Labor Statistics (Rosenfeld, 2007b). As with many economic time series, the UCR crime data could be released on a quarterly and eventually a monthly basis, with dissemination of the annual data three months after the collection year a reasonable goal. More rapid dissemination, however, would lead to a need for more imputation to develop estimates for nonreporting agencies and require corresponding improvement in the methodology for developing those imputed estimates. One attempt to significantly enhance the data from the UCR was the introduction of the National Incident-Based Reporting System (NIBRS). Rather than relying merely on aggregate counts of incidents or of ­arrestees, this approach involved compiling detailed information on individual crime incidents, the perpetrators and the victims, the multiple offenses that occurred in the incident, and aggregating those data as needed to generate population counts and rates. Participation in NIBRS by local police depart- ments has still not exceeded 25 percent of the U.S. population, even though

FACTORS CONTRIBUTING TO U.S. CRIME TRENDS 39 the system has been in operation for over 20 years. It would be most desir- able to find ways to increase that participation in a major way to develop the rich data potentially available from the NIBRS approach. One method would be to tie federal funding of state and local crime control initiatives to participation in NIBRS, with some of that funding directed specifically to NIBRS implementation. The FBI is currently developing an incident-based data system called N-DEX that involves much richer detail on each incident. It is possible that the more detailed data, especially if disseminated more rapidly, could generate much greater participation than has been the case with NIBRS. But the NIBRS experience suggests that participation is likely to be even less extensive without additional incentives. Much more can be done to improve the current minimal efforts related to crime measurement and forecasting. The precision of crime estimates from the NCVS, which was conducted initially with a much larger sample and with more face-to-face interviewing, has eroded considerably because funding limitations have reduced the sample size and resulted in more tele- phone interviews, even as declining crime rates warranted larger samples to maintain statistical power. Also, the NCVS, which now regularly provides only national estimates of victimization experience, could well provide sub- national estimates, at least for the larger metropolitan areas (see Lauritsen and Schaum, 2005). It might also be able to provide some limited number of characteristics of each respondent’s census tract if those characteristics were modified with some random error to protect the respondents’ privacy. Doing so would permit linking socioeconomic characteristics to crime prevalence. Improving the nation’s capacity to monitor crime trends will require additional resources devoted to compiling, disseminating, and updating the data. The National Institute of Justice can play an important part in this process by establishing an ongoing research program devoted to analyzing crime trends. Building the infrastructure for understanding changes in crime rates over time is an important criminal justice policy priority and a major focus of more extensive investigations of crime trends emerging from this workshop. REFERENCES Anderson, Elijah. (1999). Code of the street: Decency, violence, and the moral life of the inner city. New York: Norton. Arvanites, Thomas M., and Robert H. DeFina. (2006). Business cycles and street crime. Criminology, 44, 139-164. Baumer, Eric, Janet L. Lauritsen, Richard Rosenfeld, and Richard Wright. (1998). The influ- ence of crack cocaine on robbery, burglary, and homicide rates: A cross-city, longitudinal analysis. Journal of Research in Crime and Delinquency, 35, 316-340.

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Changes over time in the levels and patterns of crime have significant consequences that affect not only the criminal justice system but also other critical policy sectors. Yet compared with such areas as health status, housing, and employment, the nation lacks timely information and comprehensive research on crime trends.

Descriptive information and explanatory research on crime trends across the nation that are not only accurate, but also timely, are pressing needs in the nation's crime-control efforts.

In April 2007, the National Research Council held a two-day workshop to address key substantive and methodological issues underlying the study of crime trends and to lay the groundwork for a proposed multiyear NRC panel study of these issues. Six papers were commissioned from leading researchers and discussed at the workshop by experts in sociology, criminology, law, economics, and statistics. The authors revised their papers based on the discussants' comments, and the papers were then reviewed again externally. The six final workshop papers are the basis of this volume, which represents some of the most serious thinking and research on crime trends currently available.

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