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The Extent and Nature of Gang Crime

Summary and Keywords

Street gangs have been the focus of attention for over a century, largely due to their reputation for involvement in illegal activities, especially violence. Indeed, gangs use this reputation for violence as a means of survival, as they seek to intimidate others in order to protect their members from attacks from rival gangs, and to limit the willingness of community members to cooperate with law enforcement officials. Research on the nature of these groups suggests they thrive in marginalized communities, where there are high rates of poverty, family instability, and limited institutional support. Much of the information on street gangs stems from data collected in the United States, but these groups have been documented across the globe in not insignificant numbers. While gangs certainly differ in their structure and organizational capacity, these groups are routinely associated with a disproportionate involvement in delinquent and criminal acts at the local level. Perhaps most concerning, gangs and gang members are known to be associated with substantially higher rates of interpersonal violence, including homicide, than non-gang-involved persons. From a developmental perspective, even brief periods of gang membership have been found to have negative consequences across the early portion of the life course, including reduced educational attainment, lower income, family instability, and a higher likelihood of arrest and incarceration. Overall, the negative effects gangs have on communities appears to outweigh any of the short-term benefits these groups provide their members.

Keywords: gangs, gang membership, violence, homicide, delinquency

Gangs have held the interest of scholars, communities, and policymakers for over a century. There is good reason for this attention. Although once described as a primarily U.S. phenomenon, there is both official and unofficial recognition of gangs and gang members across the globe in not insignificant numbers (see, e.g., Gatti, Haymoz, & Schadee, 2011; Klein, 2001; Pyrooz & Decker, 2013). According to the National Youth Gang Survey, as of 2012, there were an estimated 30,700 gangs and 850,000 gang members throughout the United States. International Self-Report Delinquency Study estimates from countries that span northern, western, eastern, and central Europe, as well as countries in the Mediterranean and Latin America, suggest gang prevalence rates at between 0.4% and 17% of the youth population depending on the country (Gatti et al., 2011). Pyrooz and Decker (2013) found that 11.3% of their school-based sample of Chinese youth reported gang involvement. Together, these studies highlight the recognition of gangs in disparate communities and cultures throughout the globe.

It is not the mere presence of gangs that draws such focused attention, however. Rather, it is the nature and extent of crime associated with these groups that breeds concern. The evidence on the association between gangs, gang members, and crime will be reviewed to determine whether there is anything unique about the nature of offending attributable to gangs. To do so, however, requires that one understands the nature of gangs themselves, and how researchers and practitioners have come to identify and measure behaviors associated with these groups and their members. While this might seem simple, the history of gang research is replete with discussions on the characteristics that define a gang vis-à-vis other groups, and how gangs, gang members, and gang crime can be systematically identified. Understanding the complexities associated with this issue is a fundamental first step in understanding how we have come to understand the nature and extent of gang crime.

Beyond one’s ability to identify and document gangs, gang members, and gang crime, it is also important to identify the many dimensions of offending. Akin to the study of crime more broadly, the nature and extent of gang crime can be explored across multiple levels of analysis, including at the macro level, micro level, and individual level. The nature of crime is also multidimensional, including factors such as whether or not gangs or their members specialize in particular crimes, the severity of crimes associated with these groups, and the frequency of offenses attributable to gangs and gang members. To better understand the causal role of gang membership in the genesis of offending at the individual level, the timing of offending in the lives of youth will be examined, along with patterns of onset, escalation, and desistance as they relate to gang joining and leaving. The state of knowledge on various dimensions of gang crime will be explored, along those matters that are yet to be studied in the literature on the nature and extent of gang crime.

Definition of a Gang

What exactly is a gang, how is a gang member identified, and how does one identify a gang crime? These questions are important in and of themselves, as they have come to impact how both scholars and practitioners treat these groups, individuals, and actions both officially (e.g., sentence enhancements for “gang crime”) and unofficially (e.g., exclusion of “gang members” from particular groups or activities). Until we have a satisfactory definition of what constitutes a gang, how can we identify who is or is not in such a group? Similarly, if we cannot identify a gang from a non-gang group, or a gang member from a non–gang member, how can we label an action a gang or non-gang crime? Unfortunately, these matters have long been debated by scholars, practitioners, and policymakers alike, and no truly satisfactory conclusion has been identified. Yet, gangs have been the subject of popular discourse, police attention, and social intervention since at least the 19th century (Riis, 1899, 1902). In this way, we know gangs exist—gang members tell us so—but identifying the necessary or sufficient conditions that distinguish gangs from other groups remains elusive (see Ball & Curry, 1995 for an in-depth discussion).

By most accounts, the first academic discourse to deal with the definition of a gang was Frederic Thrasher’s classic study of gangs in Chicago during the 1920s. Thrasher’s desire to advance a sociological definition of a gang resulted in perhaps the most perceptive definition developed by a scholar to date (Howell, 2015; Curry, 2015), but one that is not at all practical. Thrasher defined a gang as, “An interstitial group formed spontaneously and then integrated through conflict” (Thrasher, 1927, p. 57). Thrasher (1927) goes on to provide descriptors and outcomes associated with gang development, by stating that a gang “is characterized by the following types of behavior: meeting face to face, milling, movement through space as a unit, conflict, and planning. The result of this collective behavior is the development of tradition, unreflective internal structure, esprit de corps, solidarity, morale, group awareness, and attachment to a local territory” (p. 57). Ball and Curry (1995) argued that Thrasher’s definition contains subcategories that do not meet the logic of definition, and thus falls into the category of a “synthetic definition,” given his focus on descriptive and correlational qualities of these groups. Undoubtedly, many groups, whose members would identify their group as a gang, would demonstrate group processes and emanate from a history consistent with Thrasher’s observations. Unfortunately, the ability to focus on group processes and how gangs develop is often impractical. That is, how should police, social interventionists, or researchers go about operationalizing such a definition in the field? The amount of information on a particular group’s history, internal dynamics, and behavior would simply be too troublesome to obtain to have any practical value.

Another widely cited definition of a gang is that of Klein from his 1971 study of five large gangs across Los Angeles. Klein (1971) defined a gang as:

any denotable group of youngsters who (a) are generally perceived as a distinct aggregation by others in their neighborhood, (b) recognize themselves as a denotable group (almost invariably with a group name), and (c) have been involved in a sufficient number of delinquent incidents to call forth a consistent negative response from neighborhood residents and/or enforcement agencies. (p. 13)

While this definition of a gang likely includes characteristics of most, if not all, gangs (i.e., it is exhaustive), it fails to distinguish gang from non-gang groups (i.e., it is not exclusive). A common example of where this definition failed was with respect to college sororities and fraternities. In particular, there are a number of sororities and fraternities across the globe that have a reputation for their involvement in criminal activities, which have brought forth a consistent negative response from community members and enforcement agencies (see, e.g., Bursik & Grasmick, 1993). Thus, while the definition could be applied to gangs, it could also be applied to groups not recognized as gangs by outside entities or group members themselves, and thus even Klein abandoned this definition after critics pointed out these shortcomings (Klein, 1995).

The issues surrounding defining gangs, gang members, and gang crime extend far beyond these two examples, but the purpose here is not to flesh out all of these problems. Rather, this brief discussion of definitions was meant to demonstrate that there is no consensus on how to best identify these phenomena. Without a common definition of what constitutes a street gang, the different working definitions between scholars, and across police jurisdictions, make identifying a population and collecting representative data very difficult. The most common data sources used to study gangs, such as official police data (including the National Gang Center’s former annual survey of police departments), ethnographic studies, and self-report surveys will be discussed.

Data Sources

Official gang data are available in multiple cities and jurisdictions across the country, and would ideally be a great source for gang data as each local police department often develops its own gang database to monitor gang members and gang activities. On a national level, the National Gang Center’s annual National Youth Gang Survey may have been the best way to monitor gang activity across the country, as the survey was submitted annually by local police departments across the United States between 1996 and 2012. This survey was discontinued, however, and the information is now dated. The Federal Bureau of Investigation (FBI) also collects and disseminates national gang statistics, which have been published in the 2011 National Gang Threat Assessment, and the 2013 and 2015 National Gang Reports (FBI, 2011, 2013, 2015). However, due to changes in their survey methodology, the reports are not comparable across time (FBI, 2015). Further, the difficulty from a national perspective is that each department is bound by its own local and state guidelines. Therefore, each jurisdiction maintains its own definition of what constitutes a street gang. For example, the state of Michigan identifies a group as a gang only when the state can demonstrate there are five or more people and a hierarchical command structure (State of Michigan, n.d.), whereas Iowa and many other states follow the federal definition that a group needs only three people to be classified as a gang (State of Iowa, n.d.). These differences pose problems when scholars want to generalize research findings across place and time.

A second feature of official data is that gang-related crimes are often coded for only the most serious crimes (e.g., homicide, non-fatal shootings), if they are coded at all. That is, police departments do not routinely categorize less serious crimes as involving gang members or not, and thus the only information on gang crime available is typically related to homicide. With respect to homicide, police departments tend to use either the Los Angeles definition or the Chicago definition of gang violence when classifying homicide incidents as gang related. The Los Angeles definition of a gang-related homicide identifies a homicide incident as gang related when either the suspect or victim is a known gang member. The Chicago definition, on the other hand, classifies homicides as gang related only if the incident appears to be gang motivated (e.g., retaliation, defending the gang, or initiation) (Rosenfeld, Bray, & Egley, 1999). These are two dramatically different definitions, which could potentially produce vastly different findings in regards to the number and rate of gang related homicides across cities. For example, Maxson and Klein (1990) examined homicides in Los Angeles (LA) using both the LA definition and the more restrictive Chicago definition and concluded that classifying homicides under the Chicago definition reduced the number of gang-related homicide incidents in LA by almost half. Although, when they analyzed the two definitions (LA vs. Chicago) in non-gang-related homicides they found very little difference between the two cities, and that gang-motivated homicides were extremely similar to gang-affiliated homicides.

Traditionally scholars have been critical of official police records in general, as police records are known to have recording errors and lack objectivity in how police document cases (Black, 1980). Further, research into police practices in maintaining gang records presents conflicting findings in regard to their usefulness and accuracy. Some scholars suggest police figures overestimate the impact of gangs on local crime patterns due to “moral panics,” and therefore gangs and their associated criminality are presented as problematic when it best suits the needs of the local jurisdiction (McCorkle & Miethe, 1998; Zatz, 1987). Furthermore, some scholars argue police narrowly focus on more violent individuals due to centralized gang units and gang task forces (Katz, 2001), and are therefore better able to identify and document gang involved youth who pose the greatest risk to society, while ignoring many gang involved persons who are not so problematic. For instance, in Mesa, Arizona, documented gang members accounted for nearly half of all burglary arrests and nearly a quarter of all weapons and vehicle theft arrests (Katz, Webb & Schaefer, 2000).

Additional research by Katz (2003) examined a police gang task force unit and the department’s patterns of identifying and maintaining gang lists. He determined individuals were most frequently identified as gang members through the original police report completed by the patrol officer, and this initial identification was never followed up by a gang task force member, a method purportedly in place to reduce the chance of false positives. This practice placed gang member identification solely on the patrol officer, and assumed his or her assessment was 100% correct. Further, lists were seldom purged of names of individuals who were no longer actively involved in the gang lifestyle, even though protocols were supposed to be in place to maintain the names of only those individuals who remained in the gang. These results led Katz to conclude that official gang statistics are not so much determined by formal definitions but rather by informal practices and inadequate communication between police units. In this way, identifying individual gang members through police lists may result in the over-identification of active gang members.

Early gang researchers such as Thrasher (1927), Short and Strodtbeck (1965), and Klein (1971) primarily collected data and studied gangs using ethnographic methods. Utilizing ethnographic and interview data allows researchers to gather first-hand, personal accounts on the behavior and lives of gang members, and can display a deeper understanding of the group processes that function within gangs, which is often lacking in studies that employ other data sources (Melde, 2016). Despite the depth of knowledge these data can provide, ethnographic studies do have their own set of limitations. For instance, it is hard for the researcher to discern fact from fiction, and as Klein (1971) notes, gang members are known to embellish their stories to “one-up” their friends. Furthermore, ethnographic samples are generally small, providing in-depth knowledge on only a few gangs. Therefore, data collected in this manner are not generalizable, and have unknown implications across time and place. Lastly, critics question whether simply placing an outsider (i.e., a researcher) into the natural setting of gang members can change the gang member’s behavior, or what is commonly referred to as the Hawthorne effect (Melde, 2016). Due to these limitations, researchers turned toward self-report survey methods to gain a broader understanding of gangs and gang membership.

Self-report surveys are another method of gathering data on gangs and gang members, and one that many academics use due to the lack of an agreed upon definition of a gang. An advantage of this data collection method is the ability to go directly to the source of gang membership, the individual member. Therefore, it is not an outside entity trying to determine someone’s gang status, but rather the person is able to self-identify. Survey methods also allow researchers to collect in-depth information on individual gang members and ask them questions about their involvement in violent and nonviolent acts, extracurricular activities (e.g., employment, athletics, school activities), and demographics (e.g., race, education, family composition). Relatedly, one can also gather information on involvement in crime and deviant activities that are not reported to the police, often referred to as the “dark figure” of crime. Many of the crimes not reported to police are minor offenses such as drug use and selling, and other minor delinquent behaviors that are handled in other formal institutions (i.e., schools), and are often referred to as “victimless crimes.”

Research demonstrates that self-report surveys, no matter how the question of gang membership is asked (i.e., “Do you consider your group of friends to be a gang?” Or “Are you a member of a street gang?”), produces a sample of youth who report being involved in more delinquent acts than non-gang-involved youth (Curry, 2000; Decker, Pyrooz, Sweeten, & Moule, 2014; Esbensen, Winfree, He, & Taylor, 2001; Melde, Esbensen, & Carson, 2016; Thornberry, Krohn, Lizotte, Smith, & Tobin, 2003). Additionally, survey methods allow researchers to collect a large number of surveys on gang members in a short amount of time, and across time and space. Unlike official records that use definitional standards for specific jurisdictions, which vary based on city, surveys allow for a standard measure of gang membership. The use of consistent measures through survey methods also allows for the analysis of change over time.

Although survey methods allow for the collection of information from a large sample of gang members to be gathered over a short period of time, survey methods are not without limitations. One limitation of self-report survey data concerns the validity of the information being collected from the gang members. Put simply, can we be sure gang members are telling the truth? According to a study by Webb, Katz, and Decker (2006), which examined a group of self-reported gang members during the data collection process of the Arrestee Drug Abuse Monitoring (ADAM) program, the answer appears to be yes, we can trust self-reports among gang members. Specifically, by comparing self-reported drug use and urine samples, which provide a more objective measure of the nature of the person’s drug use, Webb and colleagues concluded that gang members were just as truthful about their drug use as others in the sample, and therefore suggested that gang members were not likely to provide deceptive answers about their gang involvement. Additional research by Curry (2000) assessed the validity of self-reported gang membership by comparing self-report data to the official police gang records for the Chicago Police Department. He concluded there was a large overlap between self-reported gang membership and the gang members identified by the Chicago Police Department. He did suggest, however, that police departments identify individuals as gang members at a more conservative rate than self-report surveys (Curry, 2015).

The Extent and Nature of Gang Crime

Gangs are a noted part of the crime landscape, especially in urban environments, and have garnered a substantial amount of attention from their local communities, due to their penchant for involvement in violence. Part of this notoriety stems from the willingness of gangs and their members to be seen. In fact, gangs often purposively make their presence known to their local community through the use of graffiti, colorful clothing, and tattoos. As opposed to most criminals, or even criminal groups, who try to conceal their identity to avoid detection and apprehension, gangs openly use these signs and symbols to control others’ behavior through intimidation (Felson, 2006). That is, because people recognize that gangs are made up of sometimes large groups of people, they may be less likely to resist what appear to be gang members during interpersonal disputes or criminal events (e.g., robbery, mugging), and they will be less likely to cooperate with criminal justice officials (e.g., report crimes to the police or serve as witnesses) for fear of retaliation by the gang. Gangs use fear and intimidation in order to behave with impunity in their local community.

A particularly interesting tactic used by gangs is for disparate groups—who have no formal connection to one another—to use common names, signs, and symbols to make their presence known. Felson (2006) explained this process through what he referred to as “big gang theory.” According to big gang theory, it is much more advantageous for gangs to use established signs and symbols from large, notorious gangs, rather than to create new and unique markings. The reason is that establishing a reputation as a gang to be feared, and thus to ensure others will be sufficiently intimidated to not interfere in their criminal exploits (i.e., not resist, call the cops, or encroach on their territory), is difficult (e.g., fighting is dangerous, threat of apprehension by police) and takes time. Rather, notorious gangs (e.g., Crips, Bloods, MS-13, Latin Kings) have already established reputations that have worked to advance their criminal activities. Therefore, newly established gangs have a tendency to suggest they are aligned with larger, well-known gangs in order to use their reputation to their advantage. Felson (2006) suggested this was akin to the process of mimicry in nature, where non-threatening animals evolve to look like dangerous animals for defensive purposes. In this way, gang members are afforded the luxury of having a dangerous reputation, without ever having to develop that reputation on their own. Thus, big gang theory helps to describe how gangs use the messages delivered through the media to appear more dangerous and organized than is actually the case (Klein, 1995; Decker, Bynum, & Weisel, 1998).

A byproduct of this mimicry process, however, is that institutions in locations that face an emerging gang problem may view the problem as emanating from external sources of influence, including the purposeful migration of members of notorious gangs into new gang territory (i.e., gang franchising in new drug turf), especially immigrants and racial or ethnic minorities. Maxson (1998), who conducted the most comprehensive study on the topic of gang member migration after a period of substantial proliferation in gang activity in the 1980s and 1990s, suggested that the actual occurrence of purposeful movement of gangs from one city to the next was rare. Rather, police in Maxson’s (1998) study reported that movement of people from one city to the next was more often for social reasons than for available criminal opportunities, and that emerging gang issues were driven by local actors who formed local gangs. As Maxson (1998, p. 8) suggested, “proponents of the ‘outside agitator’ hypothesis of gang formation . . . will find little support” based on the data gathered from police across the country. Furthermore, Esbensen and Carson (2012) found that, demographically, gang members are very much akin to the local context, both from a racial or ethnic perspective, as well as with respect to immigration status. Placed in historical perspective, gangs appear to thrive in marginalized and economically distressed communities, such that the level of overrepresentation of racial and ethnic minorities is tied to their socioeconomic status.

Given this notion of big gang theory, scholars have argued that the public, including policymakers, has an irrational fear of gangs, which has led to overly punitive anti-gang legislation (McCorkle & Miethe, 2002). For example, in the early 1990s gang violence captured the attention of the U.S. House of Representatives and Senate, which held hearings in regard to the need to “do something” about gang violence. These hearings, in part, led to the 1994 Federal Crime Bill, which made being involved in a gang-related crime a federal offense. Similarly, in his 1997 State of the Union address, President Clinton stated that fighting gangs would be a top priority in his second administration (Senate, 1994, pp. 4, 19; Violent Crime Control and Law Enforcement Act of 1994, Public Law 103-322, 150001; Lane & Meeker, 2003b). To this day, gangs and the violence attributed to these groups continue to be at the forefront of federal, state, and local violence reduction efforts (see, e.g., Robbins & Rodriguez, 2017). Although gangs have clearly become a focus of political campaigns and policy, exactly how much violence can truly be attributed to gangs? And why is it gang members are known to be involved in more violence than non–gang members who live in the same community?

Research points to the role of group process as an important feature of gangs, as these processes work to create cohesion and contribute to the organizational structure of the gang (Decker, Melde, & Pyrooz, 2013). Interestingly, research suggests that most gangs remain loosely organized collectives, but there remains a significant amount of group comradery despite a lack of organizational structure. In many ways, gangs thrive through cohesion, especially in the face of conflict, where an attack on one member is viewed as an attack on the entire group, which often leads to retaliatory attacks (Decker & Van Winkle, 1996; Decker et al., 2013). In fact, Decker and Van Winkle (1996) argued that the distinguishing feature of gangs, which sets them apart from other groups—even delinquent peer groups—is the use of violence as a means of their continued existence. They argued that gangs adopt a group behavior that results in common elements and collective processes to form a group structure. For example, gang homicides are often expressive in nature and can be described through a seven-step process where real or perceived threats mobilize an event that can quickly escalate into a violent incident, which then will result in retaliation, and therefore it is likely that another violent event will occur. Additionally, a gang member’s willingness to respond to real or perceived threats from outside the group, through violence, builds group cohesion and allows the gang to maintain legitimacy in the neighborhood. Understanding the group processes of gangs is important, as it is through these group dynamics that expectations associated with gang membership are communicated, including pressure to retaliate against outsiders who have threatened the gang’s reputation as well as engage in expressive forms of violence (Decker et al., 2013). Despite the purported importance of group processes associated with gangs, there remains a dearth of empirical research in this area, and the studies on this subject offer conflicting findings. For example, in St. Louis, Decker and Van Winkle (1996) interviewed gang members and their families over a three-year period. The study revealed that many youths join gangs because they view the lifestyle as a way to enhance their reputations. Decker and Van Winkle also concluded that gangs in St. Louis did not have a strong organizational structure, and were much more loosely organized than one might suspect given popular discourse. However, violence was still a central part of gang members’ lives, despite a lack of a stable organizational structure. Violence within the gang began from day one, starting with the initiation process, and members were expected to participate in assaults and other violent incidents. For example, gang members were encouraged to use violence, or the threat thereof, as a means to avoid becoming a victim themselves. The normative expectation of aggression perpetuates a continuous cycle of violence, which can escalate to lethal outcomes. Violence, real or threatened, is even at the core of many gangs’ warnings about the consequences of leaving the gang, as members routinely report that the penalties for leaving the gang range from being “beaten out” (similar in style to having been beaten into the gang) to killed for deserting their peers.

A more recent ethnographic study by Lauger (2012) in Indianapolis, Indiana, also found that gangs are fluid, overlapping, largely unorganized, and lack stable leadership and rules. He found a similar cycle of violence as Decker and Van Winkle (1996), as new groups form and seek to claim a valued reputation on the streets, whereby gang members must be willing to fight whenever needed to both establish and maintain their group identity. Further, members in Lauger’s study (2012) preferred to commit their violent acts in a public setting, as they relied on street gossip to transmit their propensity for violence to larger networks throughout the city. The dissemination of information to the larger network is important within the inter-gang environment, as members must continuously convince others they are willing to participate in violent behavior (Lauger, 2012), or in the members’ words, to “be real gangtas.”

Venkatesh’s (1997) research offered a glimpse into a more organized street gang, where the group evolved into a more corporate-like structure. The central goal of this group structure was to maximize profits from street-level drug sales. Purportedly, this led to the tacit expectation that violence associated with the group was to be limited, and used only in instances where the group’s profits would be benefited. That is, leadership in the gang Venkatesh (1997) studied believed that violence was bad for business, as it attracted law enforcement to the area, and had the potential to disrupt drug sales. Without violence, according to local informants, police were likely to ignore drug sales and not focus on the gang as a local problem, allowing their business to flourish. Such organizational capacity, to limit individual behavior for the sake of the group profits, is not the norm for gangs that have been the focus of empirical attention.

Additional research by Taylor (1990) in Detroit identified three types of gangs: (1) scavenger gangs, which lacked consistent leadership and planning of activities, (2) territorial gangs that had an element of organization and leadership, and (3) corporate gangs, which were highly organized and focused on drug distribution. He noted that gangs could evolve through all three stages (i.e., scavenger, territorial, corporate), from unorganized neighborhood gangs to formal drug organizations. The majority of research on group structure, however, has not supported these findings of such formal gang structure, indicating that most gangs remain loosely structured (Decker & Van Winkle, 1996; Lauger, 2012).

Characteristics of Gang Homicides

Research on patterns of violence has tended to focus on homicide, even though these acts are exceedingly rare compared to other forms of violent behavior (Black, 1970, 1980; Jackson, 1990; Piquero, MacDonald, Dobrin, Daigle, & Cullen, 2005). One reason for this focus stems from the quality of the data gathered in the wake of a homicide event, and the information that can be gleaned from these data. Police agencies may be more willing to categorize homicides as gang related than other, more frequent, crimes. As a result, gang researchers are often limited in their ability to examine patterns of violence associated with gangs to these rarer events. Thus, much of the quantitative work on gangs emanating from official statistics has focused on homicide. Given the rarity of homicide in general, and gang homicide in particular across most jurisdictions, most research on the connection between gangs and homicide has occurred in very large cities, including Chicago and Los Angeles. As discussed, these two cities have been unusual in their willingness to label criminal events as gang related (i.e., the Chicago definition) or gang involved (i.e., the Los Angeles definition), and thus they have some of the most complete data on such events in all of the United States. Work by Decker and Pyrooz (2010), however, suggests that national sources can be used to conduct comparative studies across cities. They examined the reliability and validity of gang homicide data from the Uniform Crime Report (UCR), Supplementary Homicide Report (SHR), and the National Gang Center (NGC), across the 100 largest U.S. cities. They found that police-reported gang homicides are reliable and valid, and both SHR and NCG are robust measures of gang homicides.

Research by Maxson, Gordon, and Klein (1985) analyzed over 700 homicides in Los Angeles between 1978 and 1982, for both the Los Angeles Sheriff’s Department (LASD) and the Los Angeles Police Department (LAPD) to determine whether gang-related homicides differ from non-gang-related homicides. The findings suggested that gang-related homicides were more violent and visible to the public. For example, gang homicides were more likely to occur on a public street, involve firearms, and entail shooting out of a vehicle (i.e., a drive-by shooting). Further, gang-related homicides typically involved multiple offenders, had more unknown offenders—as most victims and suspects have no known prior relationship—and usually involve younger victims and offenders than non-gang homicides (Maxson et al., 1985). Additional research in Boston found that gang homicides were more spatially concentrated, and more likely to involve assaults, guns, and drugs, compared to non-gang homicides (Kennedy, Braga, & Piehl, 1997).

Using homicide data in St. Louis, Rosenfeld, Bray, and Egley (1999) administered their own coding scheme to classify gang-related homicides into gang-motivated (e.g., gang fight or gang signs), gang-affiliated (e.g., victim or suspect identified as gang member), or non-gang homicide. The results followed Maxson et al. (1985) in that gang-motivated homicides were more likely to take place in public places. Gang-motivated homicides were less likely to involve drugs compared to gang-affiliated homicides. For example, almost half of the gang-affiliated homicide incidents were drug related. Across all three homicide categories, victims and offenders were overwhelmingly black males, and homicide incidents were spatially concentrated in predominantly black neighborhoods with high levels of socioeconomic disadvantage.

Additional research, which examined homicide and gang data from St. Louis during 1994 and 1996, found that gang homicides differed from non-gang homicides on race, age, gender, weapon use, spatial concentration, victim-offender relationship, and the involvement of drugs (Decker & Curry, 2002). This research also demonstrated that gang homicides occurred within gang groups (i.e., intra-gang), not solely between different gangs (i.e., inter-gang), suggesting that gangs were somewhat disorganized in St. Louis. Other research examining a sample of 720 youth offenders who had been arrested for a gun charge over a 12-year period, found that 61 gangs were responsible for approximately 60% of all youth homicide in Boston (Braga, 2003). Additional research by Pizarro and McGloin (2006) examined homicides over a 66-month period in Newark, New Jersey, and found that homicides in that city were more akin to Decker’s (1996) violence escalation hypothesis than that of more traditional theoretical models associated with social disorganization theory.

In more recent studies, researchers have examined the spread of violence through social contagion theory, which contends that violence is transmitted much like a disease (Loftin, 1986). The social contagion process contends that peers within the same network have influence over each other and will therefore follow each other’s social cues (Burt, 1987). Furthermore, contagious epidemics have to be transmitted through a host, and for that reason social contagion is primarily based on the social structure of the network that brings people and ideas together (Gostin, Burris, & Lazzarini, 1999; Burt, 1987). Many research studies support this theory in regard to gangs and gun violence, at both the gang and individual level of analysis (see Decker & Van Winkle, 1996; Papachristos, Braga, & Hureau, 2012; Papachristos, Braga, Piza, & Grossman, 2015).

Using homicide data and gang territory maps provided by the Chicago Police Department, Papachristos (2009) was able to create a micro-level network structure of inter- and intra-gang homicide. This methodology allowed him to aggregate the homicide data from the individual level to the gang level to examine the number of deaths between and within each gang group, and to examine the length of time a dispute lasted. His findings support the idea that murders spread through an epidemic-like process of social contagion, which led him to conclude that gangs are embedded within a social network, and that violence flows back and forth between groups. The network structure of gangs appeared to create persistent conflicts between groups no matter the individual composition of membership in each gang (Papachristos, 2009).

Related research by Papachristos and colleagues (2015) examined the network structure of co-arrest data at the individual level using data from Chicago over a six-year time period. The results suggest non-fatal firearm injuries were highly concentrated within a single network, and approximately 70% of all gun violence victims were identified within these co-offending networks. Also, 89% of those victims were contained within a single component (i.e., subgroup) of the entire network. In addition, gang members were three times more likely to become a victim of such violence, suggesting they were the most susceptible to the contagion of violence through their networks (Papachristos, Wildeman, & Roberto, 2015).

Papachristos, Braga, Piza and Grossman (2015) have also examined the implications of the degree of social proximity of a gang member within a co-offending network on an individual’s risk of gunshot victimization. Using co-arrest, quality of life violations, and field interrogation records, researchers created a co-offending network of 10,531 individuals in Newark, New Jersey, over a one-year time period. Approximately 7% of the network was identified as gang members through official police records, and less than 4% of the network were victims of fatal or non-fatal gun violence. The results suggested that an individual’s risk of gunshot victimization increased the closer one was to a gang member. More specifically, being directly connected to a gang member increased an individual’s risk of victimization by 94% (Papachristos, Braga, Piza, & Grossman, 2015).

Research by Zeoli and colleagues (2014) studied the spread of homicides as an infectious disease in Newark, New Jersey, from 1982 through 2008. Results suggested firearm and gang homicides spread south and west through the city in a systematic manner over a 20-year period, while other areas of the city remained untouched by homicide clusters (Zeoli, Pizarro, Grady, & Melde, 2014). In elaborating on these findings, Zeoli, Grady, Pizarro, and Melde (2015) examined homicide data from 1997 through 2007 in Newark to determine if the movement of homicide clusters differed based on motive, across space and time. Results demonstrated that gang-motivated homicides displayed signs of diffusion, and overlapped with drug and revenge homicides, while other homicide types did not appear to follow a contagion-like process. These spatial models suggest that gang homicides are unique in how they spread across space and time, while homicides committed as a result of other motives do not appear to influence the likelihood of future homicide events.

Specialization Versus Generalization in Offending

Violence has been described as the quintessential element of gangs (Decker, 1996; Decker & Van Winkle, 1996), as it is the regularity of this behavior (or the threat thereof) that distinguishes gangs from other delinquent peer groups. Taken together with the discussion of the disproportionate involvement in homicide by gangs and their members, one might assume that violence is the only behavior engaged in by gangs. The truth is, however, that gangs and gang members do not appear to specialize in violence to the exclusion of other types of crime (Klein & Maxson, 2006). Gang member offending is actually much more generalist in nature, as gang members have been found to engage in a disproportionate number of delinquent acts of many kinds (e.g., drug, property, status), or what Klein referred to as “cafeteria style offending” (1995, p. 68). For example, a study by Thornberry (1998) examined the delinquency of gang members longitudinally, across three cities, Rochester, Seattle, and Denver. The results suggested that gang members participated in a higher rate of offenses of all types than non-gang members, across all three cities. Further, in Rochester, gang members participated in non-violent acts, such as drug use, property offending, and public order crimes at the same rate as violent offenses (Thornberry, 1998). More recent research by Gordon et al. (2004) examined youth in Pittsburgh and concluded that gang membership increased an individual’s involvement in nonviolent offenses, such as property offending, drug dealing, and substance abuse, as well as violent offending. Youth involved in gangs outside the United States are also known to participate in a variety of delinquent offenses. For instance, Gatti and colleagues surveyed over 40,000 students across 30 countries in Europe, and found that 4.4% of youth identified as being a part of a deviant youth group. The prevalence of deviant youth groups differed by country, but overall deviant youth group members were involved in delinquency, violence, and alcohol and drug use at a higher rate compared to non-deviant youth groups (Gatti, Haymoz, & Schadee, 2011).

Other scholars have examined the correlation between gang membership and drug use, in particular. For example, research by Esbensen and Huizinga (1993) found that gang membership led to an increase in drug use. They collected data through the Denver Youth Survey, and compared self-reported drug use in gang and non-gang-involved youth. Their results suggest that gang members were more likely to report using drugs such as marijuana, cocaine, and heroin. Similar findings from the Rochester Youth Development Study and the Seattle Social Development Project suggested that gang members are approximately 50 times more likely to report drug use compared to non-gang-involved youth (Battin, Hill, Abbott, Catalano, & Hawkins, 1998). A number of other studies using self-report survey methods have found that gang members are more likely to report drug use compared to non-gang members (Coffman, Melde, & Esbensen, 2015; Esbensen, Winfree, He, & Taylor, 2001; Fagan, 1989; Thornberry, Krohn, Lizotte, & Chard-Wierschem, 1993). For example, Katz, Webb, and Decker (2005) examined the relationship between self-reported drug use and gang membership using the Arrestee Drug Abuse Monitoring (ADAM) program. Their results suggested that active gang members were more likely to use marijuana and cocaine compared to former gang members.

Additional studies have used official data sources to examine the link between gang memberships and drug use, which have produced conflicting findings. For example, Zatz (1987) used court records to examine all youth documented gang members relative to a matched sample of non-gang-involved youth in Phoenix, Arizona. She found no evidence to suggest that gang members were more likely to be arrested for drug offenses than non-gang members. A study by Katz, Webb, and Schaefer (2000), which examined official data from the Mesa, Arizona, police department, however, found a significant relationship between gang membership and drug use. For example, gang members were almost three times more likely to be arrested for a drug-related offense compared to the non-gang-involved sample.

These differences in findings could be a product of the data and sample population examined, or, as Curry (2000) suggested, there may be a parallel gang problem within the United States. He suggests there are two different gang problems, one involves younger, self-reported gang members, whereas the second one involves older (i.e., adult), more violent offenders, who are more likely to be documented in official records (i.e., police reports, court records). Therefore, the conflicting findings between gang membership and drug use may not be wrong but just represent different problems throughout the country.

Gang Membership in the Life Course

Researchers have also examined whether gang membership matters from a developmental perspective. That is, does gang membership matter over the course of an individual’s life? For instance, what if individuals who join gangs already have a disproportionately high propensity to engage in crime and violence? Perhaps gang membership is not that impactful, as these individuals would be involved in antisocial behavior no matter if they joined a gang or not. This issue was described by Thornberry, Krohn, Lizotte, and Chard-Wierschem (1993), who offered three potential explanations for the elevated levels of offending associated with gang members: the selection, facilitation, and enhancement frameworks.

The selection model follows theories that seek to explain criminal behavior through relatively stable differences in criminal propensity between individuals (e.g., Gottfredson & Hirschi, 1990). In this way, gang membership is simply a display of criminal propensity, suggesting a spurious association between gang membership and crime. A common way to summarize this idea in the literature is to use the phrase “birds of a feather flock together,” suggesting that gangs are nothing more than a group of delinquent youth who associate with one another, in part as a result of their shared interests and lifestyle. If this framework is correct, then one should expect to observe a consistent difference in delinquent offending for gang-involved and non-gang-involved youth, before, during, and after being involved with a street gang. Additionally, individuals who join gangs are likely already engaged in violence, because gangs are more prone to choose such individuals for their gang, and individuals who actively participate in violence are more likely to seek out gangs (Pyrooz & Densley, 2016).

The facilitation model is more consistent with social learning theory (Akers, 1998) and opportunity theory (Osgood, Wilson, Bachman, O’Malley, & Johnson, 1996). According to the social learning perspective, individuals are exposed to specific attitudes and norms that promote delinquent behavior when exposed to gang membership. That is, individuals learn to commit crime through their primary social environment, and gangs provide a perfect atmosphere in which to learn criminal and violent behaviors (McGloin, 2008). Whereas, opportunity theory, presented by Osgood and colleagues (1996), contends that gang membership changes an individual’s routine activities, and that simply associating with other antisocial youth increases the chances of offending. For example, Haymoz, Maxson, and Killias (2014) surveyed middle school students across 19 European countries and found that delinquent offending and negative peer behaviors were the biggest risk factors in differentiating gang members from non–gang members. If the facilitation model is correct, then scholars should see increased involvement in crime only while individuals are active gang members, not before or after their time within the gang.

Lastly, the enhancement model combines the selection and facilitation models, suggesting that the processes of control, social learning, and opportunity theories are likely simultaneously at work. Thus, youth who were already involved in delinquent acts due to low self-control and low social control, become even more criminally inclined due to the group processes (i.e., social learning, opportunity theory) associated with gang membership. If this model is correct, then scholars should see individuals continuously involved in criminal offending before and after gang involvement, but the amount of offending will dramatically increase while members are active in the gang. All three models have received some support in the literature—selection (see Bjerregaard & Lizotte, 1995), facilitation (see, e.g., Thornberry et al., 1993), and enhancement (see, e.g., Matsuda et al., 2013)— but overall the enhancement model has received the most support. That is, the strongest evidence suggests that gang membership is not the starting point of an individual’s criminal offending, but that gang members have already engaged in delinquent acts, and joining a gang simply accelerated their level of offending (e.g., Melde & Esbensen, 2011; Melde, 2015).

Research by Melde and Esbensen (2011) suggested that gang membership dramatically increases levels of delinquency in the short term, and that this increase is consistent with the notion of a “turning point,” as described by Sampson and Laub (2005). In short, joining a gang restructures a person’s life in significant and lasting ways. In the case of gang membership, participants have been found to change their routine activities (e.g., unstructured socializing), as well as experience changes in their attitudes, beliefs, and emotions that increase their criminal propensity. Melde and Esbensen (2013) suggested that while gang joining led to higher rates of general offending, gang membership was particularly impactful on members’ involvement in violence, as the onset of gang membership increased the violent to nonviolent offense ratio by approximately 21%.

Since the late 20th century scholars have also studied the prevalence and extent of female gang membership, and although studies suggest females represent a minority of the total gang population, female gang members participate in a disproportionate amount of crime and violence compared to non–gang members. For example, using longitudinal panel data gathered from juveniles ages 13 through 22, Thornberry and colleagues (2003) found the lifetime prevalence of violence is 72.2% for female gang members, compared to 39% for non-gang girls. Esbensen and Huizinga (1993) studied high-risk youth over a four-year time period using the Denver Youth Survey, and found that 20 to 40% of the gang members were female, and the number of female gang members dropped as the sample aged, suggesting that females age in and out of gangs differently than males. More recently, research by Melde and Esbensen (2013) using data collected through the National Evaluation of the Gang Resistance Education and Training (G.R.E.A.T) program reported that roughly 45% of the gang members in their sample were female. Importantly, their research suggested that while male gang members had a higher criminal propensity, when compared to youth who reported gang membership at some point in the five-year study, the impact of gang membership on the propensity for violence (i.e., the increase in violent offending associated with active gang membership) was equal for males and females. This research suggests, therefore, that the impact of gang membership on males and females is quite similar among school-aged youth. Overall, in perhaps the most systematic review of quantitative information on the association between gang membership and offending done to date, Pyrooz and colleagues (2016) conducted a meta-analysis drawing upon 107 unique data sets, 179 empirical studies, and 1,649 effect sizes to determine how much gangs really matter in the genesis of criminal behavior. After accounting for a host of potential confounders, the authors concluded that gang membership has a robust association with criminal offending broadly (i.e., gang membership was associated with a 0.227 standard deviation increase in offending), indicating that the association between gang membership and offending is strong. The scientific literature on gangs, therefore, appears to suggest that these groups play an important role in shaping the behavior of their members by increasing their level of offending, including serious acts of crime and violence.

Discussion of the Literature

Research suggests that gang members participate in a disproportionate amount of violence compared to non-gang youth, and violent offending reaches its peak while youth are active in the gang lifestyle (Decker, Melde, & Pyrooz, 2013; Pyrooz, Turanovic, Decker, & Wu, 2016). When researchers examined the association between gangs and homicide, the results demonstrated that gang-involved homicides are more violent and publicly visible, are spatially concentrated in neighborhoods with high levels of socioeconomic disadvantage, and are more likely to involve drugs than non-gang-involved homicides (Maxson, Gordon, & Klein, 1985; Kennedy, Braga, & Piehl, 1997; Rosenfeld, Bray, & Egley, 1999). Despite the level of violence gang members are involved in, there is still no evidence that gang members specialize in a particular type of crime, to the exclusion of more general offending, but rather are involved in “cafeteria-style offending” (Klein, 1995, p. 68), where they are known to engage in a disproportionate number of delinquent acts involving drug offenses and property crimes. Melde and Esbensen (2013) provided evidence, however, that gang membership may lead to a disproportionate increase in violent offending, relative to involvement in other offense types.

More recently, scholars have explored the association between gangs and crime through spatial and social network analyses to determine how these groups structure offending patterns, and whether or not contagion-like processes can help explain patterns of violence associated with these groups. Results suggest that homicides indeed spread like infectious diseases, and that an individual’s risk increases the more socially connected they are to known gang members (Papachristos et al., 2015; Zeoli, Pizarro, Grady, & Melde, 2014). More research in the area of social networks is needed to further explore and understand the group and social processes associated with gangs and gang members. Indeed, due to the lack of an agreed-upon definition of a gang, in both the academic and practitioner worlds, some scholars have argued that gangs should be studied akin to any social groups, through an explicit focus on their network properties (Fleisher, 2006; Papachristos, 2006).

The study of gangs and their influence on offending highlights the complexities associated with truly understanding this phenomenon. The definitional dilemma demonstrates how difficult it can be to identify the nature of social groups in an ever-changing world. We know gangs exist, and have existed for a long period of time. Indeed, it is for this reason that gangs can rightly be considered a “natural” (Decker & Van Winkle, 1996, p. 4) phenomenon. Yet, this understanding of gangs is unsatisfying, given the myriad problems associated with these groups, both for society and the members themselves. After all, gangs appear to flourish in areas characterized by marginalization from mainstream society, in homes experiencing difficulties, and among people at risk. Unfortunately, in the long run, gangs have not been a positive solution to such issues. Thus, a continued focus on gangs and gang members is necessary, so that tangible solutions to the problems faced by those in a position where gangs offer short-term fixes for issues can be developed.

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