One of the difficult tasks in the social sciences is integrative, interdisciplinary work. There are many commonalities across the social sciences in method, theory, and policy. The study of gangs has a tradition in the U.S. that dates back nearly 100 years, with an emerging focus in Europe and other parts of the world. This Research Note argues that there is considerable overlap between the study of gangs and that of radicalized groups. Both fields examine violence conducted largely in a group context. Group structure, demographics, marginalization, strength of membership bonds, leaving the group, and the role of prison in expanding membership are all issues the two have in common. There are lessons those who study radicalized groups can take from the long tradition of gang research. This Research Note identifies twelve lessons learned (mistakes and successes) from the study of gangs that have relevance to the study of radicalized and extremist groups.
Keywords: gangs; criminology; terrorist groups; organized crime; terrorism research.
How can the study of gangs, gang members, and gang crime provide insights and guidance for the study of radicalization, extremism and terrorism? It is our contention in this short Research Note that lessons learned in the study of gangs have direct applicability to understanding terrorist groups and acts. While the study of political radicalization has a long tradition, the recent global concern over terrorism has focused increased attention and resources on the issue. Many criminologists paid little attention to acts of terror prior to the September 11, 2001, attacks in the United States. Thus there has been some “catching up” in understanding radicalization and extremism, with several independent groups of scholars holding that much can be learned through the comparative study of radicalization and extremism with other groups of criminological, political, and sociological relevance.
The study of gangs and radicalized groups share a great deal in common. The two fields of research are similar in that they both study hard-to-reach populations that engage in criminal actions. Both groups are composed primarily of young men. Gangs and terrorist groups tend to be loosely organized as opposed to maintaining rigid organizational hierarchies. The violence that these groups engage in is public and involves victimization and harm to members of the general public. The violence used by gangs and radicalized groups is also disproportionate to the degree of harm, marginalization, or disrespect experienced among extremists or gang members. Group processes are central to the processes of recruitment, the engagement in violence, mobilization and forms of collective behavior. In both the study of gangs and terrorism there is a “dark” figure of crime, that is, the volume of crime engaged in by these groups is not well known or understood. Much like terrorism, the study of gangs is also plagued by a number of “myths”. Such myths (gangs are well organized, gangs control drug sales, gang membership is permanent, gangs are organized globally, only males join gangs etc.) created misunderstandings of what gangs, gang members and gang crime are like. 
Of course, there are important differences between gangs and terrorist groups. Notably, gangs generally lack political beliefs and ideology, violence among terrorists has a different motive than that of gangs, and the international component to terrorism differentiates it from the vast majority of local gang activity. There is another difference between gangs and terrorism that is revealed in two recent reviews of the respective literatures. Kris Christman’s systematic review of the literature on religious radicalization and violent extremism included 319 works, six of which were published in the 1980s and fourteen in the 1990s. This illustrates the recency of research on such groups. The literature on gangs, on the other hand, is comprised of around 5,000 works that date prior to the 1920s with a fifty-year tradition of empirical research, illustrating the long history gang research has come from.  It is against this background that gang research might offer some insights (and mistakes) to research on terrorism and radicalization. Indeed, despite some of the substantive differences between gangs and terrorism, we posit that the overlap is consequential for both areas of study.
This Research Note therefore identifies ways that the study of gangs can inform the study of terrorism, radicalization, and extremism. We examine the overlap between the two areas primarily by focusing on what research on terrorism and radicalization might learn from the history and evolution of gang research. We specifically identify twelve “lessons learned” from gang research that can inform research into terrorism and extremism. Given the long history of studying gangs, and the sheer magnitude of the literature, there are several areas of research that the study of these topics can look to, to find methods, theory, and policy to speed the process of developing models and ways to study these important topics.
Lessons Learned in Gang Research: The Good, the Bad, and the Ugly
The principles of sound research are equally applicable to a number of areas of inquiry. There are some aspects of social science research, however, that are more important to the study of groups. This includes radicalized extremist groups and gangs. We proceed by identifying twelve principles, in no particular order of significance, derived from gang research that we believe are applicable to research on groups involved in terrorism or radicalized groups. We remind readers that gang research has not reached some broad or final consensus and that there are both strengths and weaknesses in this literature. To be sure, there are also aspects of research on terrorism and extremism that can inform gang research.
First: triangulation of ideas and methods. Multi-method, multi-disciplinary studies paint a more diverse and accurate picture of gangs than single method studies; the same is true of terror groups. Much research on gangs depended on either ethnographic studies of a small number of gangs or gang members or law enforcement data. Moreover, the study of gangs originated in the discipline of sociology (Frederic Thrasher). While much of the research on gangs in the last two decades is found in criminology, there is a much more interdisciplinary flavor to the study of gangs today than even as recently as the turn of the century. Of course, triangulating ideas and methods is easier said than done.
Triangulation of multiple data sources is particularly important in a nascent area of research; it allows researchers to describe the group from multiple perspectives and more fully assess the reliability and validity of information. Through the use of multiple data sources, gang researchers learned that gangs have many more females, are younger and more diverse when it used school surveys of gang members rather than relying solely on law enforcement data. Combining several methods (trial transcripts, Lexis-Nexus, scenarios, experiments, survey research, school, law enforcement, prison and jail data) pushed the field of gang research ahead. Much of the best research and most developed substantive areas of study on gangs comes from studies that have combined multiple sources of data. Among the best examples is Jim Short and Fred Strodtbeck’s Youth Studies Program in Chicago from the 1960s, which combined gang-level data and field notes from detached workers, youth personality inventories and self-reported activities, police records and census reports. A contemporary example is found in the work of Beth Huebner and her colleagues in St. Louis, who combined geocoded data from law enforcement gang intelligence on gang member residences, police records of gun assaults and gun seizures, medical examiner records of drug-related deaths, and U.S. Census data on neighborhood structural conditions. Triangulation often calls for innovative methods, such as the use of social media like Facebook, Twitter and YouTube. Indeed, research on terror groups is more sophisticated than the study of gangs on this particular issue. Much terrorist research now is based on data pulled from such social media. The external validity of such data is hard to establish, which is why it is important to combine, for example, online resources with survey or ethnographic methodologies.
Second: understand the symmetries and asymmetries across the selection and the (dis-) engagement processes into and out of groups. Gang studies paid virtually no attention to the process of getting out of the gang until recently. So much attention was paid to the risk factors for gang membership and the consequences of gang membership that few realized that the youth and young adults who join gangs invariably leave gangs. It is therefore important to find out what prompts disengagement and whether the disengagement process is the inverse of selection into gangs. If joining gangs is characterized by illicit opportunities, excitement, gang networks, and status voids, would conventional replacements facilitate disengagement? Gang research found that natural social processes—disillusionment with gang life, maturation, family, romantic relationships—had a good deal to do with getting out of the gang. Dramatic departures were rare as most members just “walked away.” This research was bolstered by longitudinal research that demonstrated gang membership was generally of short duration, typically less than two years. Extremism research has shown more interest in the disengagement process and the findings from this work are generally consonant with that of the study of gang disengagement. Linking the process of disengagement from groups to life course theory has also proven to be valuable. Doing so contextualizes the role of gang membership in the life course rather than viewing it as static with no attention to the dynamics of life change. Such an analytic lens also underscores that the vast majority of gang members move past their time in the gang to more traditional activities.
Third: study the collective—the clique, cell, group, or organization—do not just pay lip service to it. The study of gangs has taught us time and again that the group is more powerful than the individual. Because groups motivate individuals to act in ways they would not otherwise do, it therefore is critical to understand the collective features of the group and how it relates to crime and deviance. Group structure differs from gang to gang and is not monolithic, which is why it is equally important to understand the role of group process within the group. Focusing on group process naturally leads to asking questions about the catalysts for actions of various sorts. Identifying the steps in engaging in violence, whether in the gang or terror context is important. Both individual and group motivations are important. Understanding the role of group process and organizational structure in recruitment, adopting group norms and engaging in violence are key issues in understanding both gang and terror groups and acts. It is important not to squabble over generalizing whether extremist groups are hierarchical, decentralized, or leaderless, but instead to determine how each of the organizational structures relate to different group processes and accordingly different collective and per capita rates of crime and deviance. Admittedly, gang research has largely come up short in studying gangs as groups, instead opting to studying gang members as individuals. We would encourage extremist research to pay strong attention to units of analysis and, what we describe next, levels of explanation.
Fourth: definitions matter. Consistent, validated definitions of gang members, gangs and gang activities are relatively recent in gang research. Such definitional clarity is needed for understanding terrorism, radicalization, and extremism. Indeed, definitions of groups and behavior are the core of a scientific approach to understanding phenomena. A better understanding of the differences within and between groups involved in terrorism as well as groups involved in crime more generally is important to understanding how to respond to such groups. Individuals, groups, and group activities need to be distinguished clearly, as advised by Jim Short. Paying attention to the clear definitions of concepts is key to moving a solid agenda of research on groups of all types ahead. For example, the words terrorism, radicalization and extremism are often used inter-changeably yet these refer to quite different phenomena. A typology of extremism would differentiate between political extremism, religious extremism, environmental extremism, and other forms of extremist beliefs. This raises the important question of whether extremist groups—as well as extremist individuals—are defined by their beliefs or by their behaviors. Gang research has struggled over the years with tautological critiques about the extent to which crime (and even violence) should be included in the definition of a gang. If behavior is a definitional requirement it will change the meaning and magnitude of the problem. An example of this is found in Cheryl Maxson and Malcolm Klein’s study of gang homicides, where there found that shifting the definition from motive-based (i.e., homicide to further the collective goals of the gangs) to member-based (i.e., a gang member was involved) produced twice as many gang homicides. We think this has important implications for the study of violent extremism, as illustrated in the comparison of the Suicide Attack Database and the Global Terrorism Database in the Washington Post. Efforts should be made to assess the reliability and validity of databases across units of analysis.
Fifth: do not forget the women. Gender matters a great deal for gang activity and group process. While men comprise the largest group of gang members and terror groups, women exert considerable influence on the behavior and membership of such groups. There is a reason that the cover to John Horgan’s book is so captivating, almost shocking—it is unexpected that a woman, smiling with a head cover while holding a weapon, would ever be “walking away from terrorism.” In this context, we encourage terrorism research not just to “add gender and stir,” which means going behind simply the concentration on acts of terror and the similarities of male and female radicalized extremists. Rather, this means attempting to understand how gender is used to instigate conflict, when it is used as a strength, and when it is–on balance – a source of a weakness in extremist groups. These are issues the gang literature has confronted, albeit not perfectly, for some time.
Sixth: knowledge of the efficacy of programs should be proportional to the investment in such programs. It is curious that interventions are not well understood or evaluated in the gang world. Malcolm Klein and Cheryl Maxson lament in their review of program evaluation that everything is “promising”. That said, everything can not be promising. The experience from gang interventions is that there has been forty years of interventions and very few high quality evaluations. Perhaps as much as $100 million has been spent on gang programming and yet we still do not know what works. Programs, policies, and interventions in the terrorism world need to have serious full-scale evaluations, or run the risk of following the futile path of an abundance of ‘promising’ evaluations attempts at a great expense to funding agencies. This is a tall task in the area of extremist research, where empirical findings rarely come with a control group let alone move outside of the realm of case studies. When rigorous evaluation is hard to come by, it would be profitable to take advantage of natural experiments–random or exogenous shocks–to assess the efficacy of policies and programs.
Seventh: distinguish instrumental from symbolic activities. This relates to our point above about definitions, yet is worthwhile to emphasize it also in the context of motive and method. There is a great deal of braggadocio and symbolic violence in gangs and much less instrumental violence. Separating the one from the other is important for theory and policy alike. Similarly, there is a great deal more “talk” about gang violence than actual violence and a lot more talk about “being hard” and riding “missions’ for the gang than occur (i.e., “I’m down for a Jihad”). Indeed, gang life is often portrayed as exciting and glamorous and extremist life as “five-star jihad” and revolutionary. The symbology of gangs as well as terror groups has been greatly enhanced by the expansion of online outlets and social media. It is now easier than ever before for gangs and terror groups to express violent messages, whether or not they actually intend to act on those messages. Often the threat of violence – for both gangs and terror groups – is enough to accomplish an objective. Researchers need to integrate approaches to include this reality into their methodology, particularly because official sources tend to exaggerate the extent of the problem and violence related to it. This is counter-productive as it gives groups more recognition than they merit and recognition is an important commodity to such groups,
Eighth: research must be held accountable for false positives and false negatives. Gang research has not done a good job of assessing risk for involvement in crime. We can say with great confidence that gang membership increases criminal behavior—there are scores of studies with rigorous methodology that lend support to such as conclusion. However, not all gang members are criminals and not all criminals are gang members. That is, we know a lot about how rates of criminal behavior are higher between gang and non-gang populations as well as how this behavior changes upon entering and existing gangs. Yet little is known about distinguishing high-rate gang offenders from low-rate gang (and from non-) offenders. The message here is that research on terrorism and radicalization should assess risk carefully and assign interventions accordingly. Phelan Wyrick identifies a “pyramid” of problems and responses, arguing that the small number of the most serious offenders should receive the most serious of interventions. This has served to focus intervention and prevention efforts more effectively and efficiently. This harkens back to the point that blanket labels of “gang member” or “radical” (or extremist) should be used with caution or used in tandem with behaviors rather than beliefs. Indeed, following the conclusions John Monahan reached on terrorism risk assessment is a good pathway forward, but issues of over- and under-identification will remain problematic.
Ninth: understand the network of opposition underpinning extra-legal groups. Gangs are oppositional groups that thrive on enemies and conflict, real and constructed. Indeed, no gang could survive without a rival. There is a reason that it is almost impossible to find a city with only one gang. Conflicts and enemies spawn an oppositional culture – a culture in which defeating enemies is more important than achieving goals. Without such elements of an oppositional culture, gangs could not exist. This oppositional aspect of gangs has a direct referent to groups that engage in terrorist activities. The symbols, activities, and causes of radicalized groups reflect their oppositional nature. In most cases the government or certain cultures is the rival for terrorist groups and often a major goal of such groups is to provoke a reaction or in some cases an over-reaction. Indeed this is one of the areas where the correspondence between terrorism and gang research is the strongest: both need enemies to exist and grow.
Tenth: there is a need for theory making and theory testing. Where advances have been made in the study of gang worlds, these reflect equilibrium between theory making and theory testing. Any tilt in the scales will either lead to the over- or under-abundance of ideas that will advance the literature. This was the case in the “golden era” of gang research around 1960, when sociological theory was steeped in the culture of the gang. Yet as Malcolm Klein noted about the state of gang theories in the 1960s: “many of the theoretical statements about gangs currently so widely accepted as fact are nothing of the sort. Rather, they are either undemonstrated, non-demonstrable, or actually demonstrated to be in error.” Likewise, much of the gang research over the last twenty years has moved toward empiricism, mostly at the individual-level study of gang members, at the expense of advances in theory. The extremism literature appears to suffer from an over-abundance of theory and an under-abundance of testing. The fact that terrorist acts are rare events in most countries, as are radicalization processes and extremist beliefs, violent extremist researchers are hard pressed to have access to readily available data sources, let alone data capable to testing theories. The survey and longitudinal research revolution in the social sciences in the 1980s and 1990s set in motion an explosion of gang research (actually, gang member research) based on many of the ideas and theories found in the fieldwork and theories of prior decades.
Eleventh: pay close attention to the role of prison. This is an area of gang research that needs development in method, theory and policy. Access to inmates is often not easy and even when authorities cooperate with research, subjects are often reluctant to be interviewed. It is well-established that the disorganized street gang member comes out of prison with more discipline, having been a member of a more organized gang in prison. The structure of prison gangs and the development of well-disciplined roles in such groups elevate gang members and their gang to a different, more organized state. We know that while in prison, gang members change both behavior and attitudes. In the U.S., prisons have been the site of producing radicalized beliefs including religious extremism, anti-government extremism and the tenets of hate groups. There is some evidence that imprisonment plays a role in radicalizing individuals and “producing” terrorists. As little as we understand about the role of imprisonment on radicalization, we understand even less about the transition from prison to the street on the part of gang members and extremists. Further, prison gangs often stay in touch with their street gang and gang associates through the re-cycling of individuals through prison and other communication methods. Such links between the street and the prison, the prison and the street are important mechanisms of the transmission of motives, methods and radicalized beliefs.
Twelvth: comparative research will offer greater returns to knowledge than research conducted in isolation. A special emphasis should be placed on the emergence of groups and cultures and how they each differ in form and function. The field of public health inquires whether close contact is required for the transmission of disease. Do gangs and extremist group spread through direct contact with other gang members or extremists or are there some alternative dissemination mechanisms? This was a key issue for gang researchers in the 1980s and 1990s when gang activity expanded greatly across the United States. It was necessary to determine whether gangs were franchising into new territories or whether gang symbology was being adopted by marginalized youth. An analogous vein of this problem is found in Latin America for “pandilla” (i.e., homegrown, localized) and “mara” (i.e., transnational roots, deportation) gangs. These very questions are of unquestionable import to the study of terrorism, radicalization, and extremism, especially with the increasing importance placed on the movement of extremist persons (e.g., foreign fighters) and the transmission of extremist beliefs (e.g., homegrown radicals). By its nature research on terrorism and extremism is comparative and crosses state boundaries, yet a comparative research agenda is ripe for addressing questions that reach the very core of the study of extra-legal groups. The gang world has only recently embarked on such an agenda with the emergence of the important Eurogang research platform. That platform can be a model for developing consensus definitions, methods, and international collaboration efforts.
There are many points of divergence between the study of, and response to, gangs and groups involved in terrorism. That said, the points of overlap are so substantial that it would be disappointing not to learn from the successes (and the many failures) of gang research. These include characteristics of the individuals involved, the groups and their activities. We would advocate for a theoretical platform organized around Jim Short’s levels of explanation and a comparative research platform organized along the lines of the Eurogang program of research. Together this would provide a collection of ideas and theory and a core methodological basis to study them.
It took gang research nearly 100 years to reach a semblance of a solid base of scientific knowledge. Malcolm Klein lamented that it took gang research too long to get there and that this process would have been hastened with greater loyalty to a comparative research agenda. Indeed, one only has to look at the homicide counts in the U.S. and see that there have been over 30,000 gang-related deaths since the 1990s to agree with the sentiment expressed by Klein. The threat of extremism and terrorism is too great to ignore the success or repeat the missteps of gang research, practice, and policy.
 The phrase “I’m Down” is common street parlance for “I am in agreement with” or “I will do that”.
We are grateful to the helpful comments of the reviewers and Paul Gill, co-editor of this issue of Perspectives on Terrorism. Dr. Gary LaFree (START Center) also provided valuable feedback. Errors and shortcomings remain the province of the authors.
 Richard Rosenfeld (2004), ‘Terrorism and Criminology,’ In Mathieu Deflem (Ed.), Terrorism and Counter-Terrorism: Criminological Perspectives, (London: Elsevier) pp. 19–32.
 Examples include: Mary Beth Altier, Christian N Thoroughgood, and John G Horgan (2014), ‘Turning Away From Terrorism: Lessons from Psychology, Sociology, and Criminology, Journal of Peace Research 51(5): pp. 647 – 661; Maura Conway (2007), ‘Terrorism, the Internet, and International Relations: The Governance Conundrum.’ In: Dunn, Myriam, Victor Mauer, and Felisha Krishna-Hensel (Eds.), Power and Security in the Information Age: Investigating the Role of the State in Cyberspace (London: Ashgate), pp. 95 – 127; Scott H. Decker and David C. Pyrooz (2011), “Gangs, Terrorism, and Radicalization,” Journal of Strategic Security, 4: 151 -166; Scott H. Decker and David C. Pyrooz (2014), “Gangs: Another Form of Organized Crime?” in Letizia Paoli (Ed.), Oxford Handbook of Organized Crime (Oxford: University Press); John G. Horgan (2008). ‘Deradicalization or Disengagement?’ Perspectives on Terrorism 2(4): pp.1-5; Gary LaFree and Laura Dugan (2004), ‘How does studying terrorism compare to studying crime?’ In Mathieu Deflem (Ed.), Terrorism and Counter-Terrorism: Criminological Perspectives, (London: Elsevier), pp. 53–74.
 These myths were identified originally by James C. Howell (2007). Menacing or mimicking? Realities of youth gangs, Juvenile and Family Court Journal, 58(2), 39-50; see, for an international comparative take on gangs and violence, Scott H. Decker and David C. Pyrooz (2010), ‘Gang Violence Worldwide: Context, Culture, and Country. In Glenn McDonald (Ed.), Small Arms Survey, 2010 (Cambridge:University Press), pp. 128 -155.
 Kris Christman. (2012). Preventing Religious Radicalization and Violent Extremism: A Systematic Review of the Research Evidence. Youth Justice Board for England and Wales.
 David C. Pyrooz and Meghan M. Mitchell (2015), ‘Little Gang Research, Big Gang Research.’ In: Scott H. Decker and David C. Pyrooz (Eds.). The Handbook of Gangs. (New York: Wiley), forthcoming.
 Frederic M. Thrasher (1927), The gang: A study of 1,313 gangs in Chicago. Chicago: University of Chicago Press.
 Examples are found in the following works: Brenda C. Coughlin and Sudhir Venkatesh (2003), ‘The Urban Street Gang After 1970,’ Annual Review of Sociology, 29: 41 – 64; Liran Goldman, Howard Giles, and Michael A. Hogg (2014), ‘Going to Extremes: Social Identity and Communication Processes Associated with Gang Membership.’ Group Processes & Intergroup Relations 17(6), pp. 813 – 32; Jane Wood, and Emma Alleyne (2010), ‘Street Gang Theory and Research: Where Are We Now and Where Do We Go from Here?’ Aggression and Violent Behavior 15 (2), pp. 100 – 111; Karen Joe-Laidler and Geoffrey P. Hunt (2012), ‘Moving Beyond the Gang-Drug-Violence Connection,’ Drugs: Education, Prevention and Policy, 19 (6), p. 442–452.
 James F. Short Jr. and Fred L. Strodtbeck (1965), Group Process and Gang Delinquency, Chicago: University of Chicago Press. See the recent review of Jim Short’s work, particularly the YSP project, in; Lorine A Hughes (2015), ‘The Legacy of James F. Short, Jr.’ In Scott H. Decker and David C. Pyrooz (Eds.). The Handbook of Gangs. (New York: Wiley), forthcoming.
 Beth M. Huebner, Kimberly Martin, Richard K. Moule Jr, David C. Pyrooz, and Scott H. Decker (2014), ‘Dangerous Places: Gang Members and Neighborhood Levels of Gun Assault,’ Justice Quarterly, forthcoming. DOI: 10.1080/07418825.2014.984751
 Maura Conway (2006), ‘Terrorism and the Internet: New Media—New Threat?’ Parliamentary Affairs, 59 (2), pp. 283–298.
 Nick Bilton (2014, August 27), ‘Ferguson Reveals a Twitter Loop.’ New York Times.
 Scott H. Decker, David C. Pyrooz, and Richard K. Moule Jr. (2014), ‘Disengagement from Gangs as Role Transitions,’ Journal of Research on Adolescence 24 (2): 268–83; David C. Pyrooz andScott H. Decker. 2011; ‘Motives and Methods for Leaving the Gang: Understanding the Process of Gang Desistance,’ Journal of Criminal Justice, 39(5): 417-425.
 Tore Bjorgo and John Horgan (Eds.), (2008). Leaving Terrorism Behind: Individual and Collective Disengagement, New York: Routledge; John Horgan (2009). Walking Away From Terrorism: Accounts of Disengagement From Radical and Extremist Movements, New York: Routledge; Gary LaFree and Erin Miller (2008), ‘Desistance from terrorism: What can we learn from criminology?’ Dynamics of Asymmetric Conflict, 1(3), 203-230.
 Marc Sageman (2004), Understanding Terror Networks. Philadelphia: University of Pennsylvania.
Marc Sageman (2008), Leaderless Jihad: Terror Networks in the Twenty-First Century, Philadelphia: University of Pennsylvania.
 James F. Short, Jr. (1985), ‘The Level of Explanation Problem,’ In Robert F. Meier (Ed.), Theoretical
Methods in Criminology (Beverly Hills, CA: Sage), pp. 51-74.
 Malcolm W. Klein and Cheryl L. Maxson (2006), Street Gang Patterns and Policies, New York: Oxford University Press.
 Cheryl L. Maxson and Malcolm W. Klein (1990), ‘Street gang violence: Twice as great, or half as great?’ In: C. Ron Huff (Ed.), Gangs in America (Newbury Park, CA: Sage), pp. 71-100.
 Representatives of the Chicago Project on Security and Terrorism wrote a critique of the Global Terrorism Database, collected and maintained by the National Consortium for the Study of Terrorism and Responses to Terrorism, saying that it exaggerated the number of terrorist attacks due to shifting methodology (). In a response by the senior staff from START, they pointed out that regardless of methodology, there is overwhelming overlap, with correlations around 0.90 or greater, despite independent methodologies (). We see these debates as a healthy sign for the advancement and growth of the terrorism literature.
 Feminists such as Meda Chesney-Lind and Joanne Belknap argue that criminologists’ simply added gender to their models without attempting to fully understand the differences in role and meaning for women’s involvement in crime .- Joanne Belknap, J. (2007), The invisible woman: Gender, crime, and justice (3rd ed.). Belmont, CA: Wadsworth; Meda Chesney-Lind (1997), Girls, women, and crime. Thousand Oaks, CA: Sage.
 Some of the best work on this topic includes: G. David Curry (1998), ‘Female Gang Involvement.’ Journal of Research in Crime and Delinquency, 35(1), 100-118; Panfil, Vanessa, and Dana Peterson. 2015. Gender, Sexuality, and Gangs: Re-envisioning Diversity. In Scott H. Decker and David C. Pyrooz (Eds.), Handbook of Gangs. New York: Wiley; Jody Miller (2001), One of the Guys: Girls, Gangs, and Gender. New York: Oxford University Press; in particular, see Mac Klein’s forward to Jody Miller’s book, where he acknowledges how ignoring women misses out on roughly one quarter of the gang population. Malcolm W. Klein, M.W. (2001). Forward. In J. Miller’s One of the Guys: Girls, Gangs, and Gender. New York: Oxford University Press.
 Malcolm W. Klein and Cheryl L. Maxson (2006), Street Gang Patterns and Policies, New York: Oxford University Press; Jason Gravel, Martin Bouchard, Karine Descormiers, Jennifer S. Wong, and Carlo Morselli (2013), ‘Keeping Promises: A Systematic Review and a New Classification of Gang Control Strategies. Journal of Criminal Justice, 41(4), pp. 228–242.
 Malcolm W. Klein and Cheryl L. Maxson (2006), Street Gang Patterns and Policies, New York: Oxford University Press.
 The work of Scott H. Decker and Barrik Van Winkle and Jack Katz illustrate this. Scott H. Decker and Barrik Van Winkle, B. (1996), Life in the Gang: Family, Friends, and Violence. Cambridge: University Press.
 Maura Conway (2010), ‘Terrorism and the Internet: A Review of the History, Issues, and Responses.’ In: Pauline Reich (Ed.), Cybercrime and Security (Oxford: University Press).
David C. Pyrooz, Scott H. Decker, and Richard K. Moule Jr. (2013), ‘Criminal and Routine Activities in Online Settings: Gangs, Offenders, and the Internet.’ Justice Quarterly, forthcoming. DOI:10.1080/07418825.2013.778326;
Gabriel Weimann (2004), http://www.terror.net: How Modern Terrorism Uses the Internet. Washington, DC: United States Institute of Peace.
 Phelan Wyrick (2006). ‘Gang Prevention: How to Make the “Front End” of Your Anti-Gang Effort Work,” U.S Attorneys’ Bulletin 4(3), pp. 52–60.
 These conclusions included: (1) clear definitions of the terrorist activities to be studied, (2) tailoring the development of the identification risk factors to terrorism particularly and not violence generally, (3) focusing on building a knowledge base on “robust” risk factors most likely to be related to terrorism, and (4) developing an infrastructure of access to terrorists and non-terrorists to establish the validity of risk factors. See John Monahan (2012), ‘The Individual Risk Assessment of Terrorism,’ Psychology, Public Policy, and Law, 18(2), 167-205.
 Marc Sageman (2004). Understanding terrorist networks. Philadelphia: University of Pennsylvania Press;
Marc Sageman (2008). Leaderless jihad: Terror networks in the twenty-first century. Philadelphia: University of Pennsylvania Press.
 Tore Bjorgo (2013), Strategies for Preventing Terrorism, New York: Palgrave.
 Malcolm W. Klein (1971). Street Gangs and Street Workers. Englewood Cliffs, NJ: Prentice-Hall,p. 28
 Scott H. Decker, Chris Melde and David C. Pyrooz (2013), ‘What do we know about gangs and gang members and where do we go from here?’ Justice Quarterly, 30 (3), pp. 369–402.
 Randy Borum (2011), ‘Radicalization into Violent Extremism I: A Review of Social Science Theories.’ Journal of Strategic Security, 4(4), 7-36; Donatella Della Porta, and Gary LaFree (2012), ‘Processes of Radicalization and De-Radicalization,’ International Journal of Conflict and Violence, 6, pp. 4 -10.
 Dina Temple-Raston (2015), “French Prisons Prove to be Effective Incubators for Islamic Extremism,” Parallels, January 22.
 Mark Fleisher and Scott Decker (2001), “An Overview of the Challenge of Prison Gangs,” Correctional Management Quarterly, 5, 1-9.
 Malcolm W. Klein and Cheryl L. Maxson (2006), Street Gang Patterns and Policies, New York: Oxford University Press.
 The Eurogang homepage is hosted by the Department of Criminology and Criminal Justice at the University of Missouri-St. Louis (). The Eurogang manual provides an excellent overview of the Eurogang program of research. Frank M. Weerman, Cheryl L. Maxson, Finn-Aage Esbensen, Judith Aldridge, Juanjo Medina, and Frank Van Gemert (2009), Eurogang Program Manual: Background, Development, and Use of the Eurogang Instruments in Multi-Site, Multi-Method Comparative Research. Retrieved from
 Malcolm W. Klein (2005), ‘The Value of Comparisons in Street Gang Research,’ Journal of Contemporary Criminal Justice, 21 (2), pp.135 – 152.
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