Wesley G Jennings & Alex R Piquero. 21st Century Criminology: A Reference Handbook. Editor: J Mitchell Miller. Sage Publication. 2009.
The relationship between age and crime has been among the most researched of all “facts” in criminology (Farrington, 1986a; Hirschi & Gottfredson, 1983). Furthermore, it also has been—and continues to be—one of the most contentious of all issues, with researchers expressing different views about its meaning and interpretation. More specifically, the robust nature of the relationship between age and crime gives rise to the question of whether the degree to which the aggregate pattern displayed in the age-crime curve (i.e., with crime rising to a peak in the late teens and then declining more or less in the early 20s) is more similar or different from the pattern of individual careers.
Acknowledging the long history of scholarly attention to understanding the age-crime curve, a substantial amount of information has been generated with regard to the onset, persistence, and desistance associated with criminal offending over the life course. In the same vein, this rich research has fostered the development of theories of crime that have been proposed across a number of social science disciplines. The commonality that is evident across these theories is that they seek to explain the fluctuations in criminal activity over the life course as well as offer assumptions as to how and why individuals may vary in their involvement in crime and deviance across key developmental phases of the life course.
The purpose of this chapter is to provide readers with an overview of what has been termed life course criminology. The chapter begins with a brief overview of the criminal career framework and provides some empirical evidence on what is known about criminal offending over the life course based on the research findings gleaned from some of the most notable studies in this area. This section is followed by a discussion of the origin of the life course paradigm as we know it today, including its roots in sociology and psychology, which subsequently led to the emergence of the developmental/life course criminology (DLC) paradigm in criminology in particular. Following a review of several key DLC theories, this chapter concludes with a brief presentation of the gaps in the current DLC literature and offers several suggestions of where future research in this area should proceed.
To understand what crime over the life course actually means for research and practical purposes, it is important to become familiar with the criminal career terminology. In its most rudimentary form, a criminal career is the “characterization of the longitudinal sequence of crimes committed by an individual offender” (Blumstein, Cohen, Roth, & Visher, 1986, p. 12). As the word longitudinal implies, there is an inherent time dimension to criminal careers. Furthermore, this suggests that there are identifiable start and end points that allow researchers to chart out an individual’s criminal career length.
The criminal career paradigm acknowledges that certain individuals start their criminal activity at one particular age, continue to commit various crimes for some period of time, and then essentially quit offending. Considering this assumption, the criminal career framework suggests the need to examine causes and correlates related to why and when individuals start offending (onset), why and how they continue offending (persistence), why and whether offending becomes more frequent or serious (escalation) or specialized, and why and when people stop offending (desistance).
Although one of the earliest criminal career studies was the qualitative depiction of delinquency presented by Clifford Shaw (1930) in The Jack Roller, criminal career research soon turned noticeably quantitative. Sheldon Glueck and Eleanor Glueck’s pioneering work, 500 Criminal Careers (1930), and a follow-up study entitled Unraveling Juvenile Delinquency (1950) provided criminologists with the most definitive and detailed source on the correlates of crime and how crime fluctuated over the life course among 500 delinquent and 500 matched control youth growing up in Boston. Not only was the Gluecks’s study unique and rigorous in its methodological design, but also the data provided by the Gluecks were considerably comprehensive. For instance, the Gluecks collected a wealth of information from self-reports (participant, parent, and teacher interviews) and gathered data from official records (police, court, and corrections). Thus, the richness of these data was unprecedented in its time and served as one of the key sources for criminological theorizing for some time. It continues to inform criminological theory today.
Quite some time after the Gluecks’s pioneering efforts, Marvin Wolfgang and his colleagues successfully completed one of the most well-known studies to date of the longitudinal progression of crime over the life course. This research, referred to as the Philadelphia Birth Cohort Study (Wolfgang, Figlio, & Sellin, 1972), was a retrospective study of criminal activity among all 9,945 males born in the city of Philadelphia (with continual residence through age 17) in 1945. Although the study was limited in that it contained only basic demographic information and relied solely on official sources of data, two of its key findings were groundbreaking at the time. The first important finding was that nearly one third of the cohort had an official police contact by age 17, and most of these offenders were “one-timers” in that they did not accumulate another police contact after their initial offense. Second, and perhaps more important, Wolfgang et al. discovered that only 6% of the cohort and 18% of the cohort’s offenders were responsible for committing roughly half of all the offenses and about two thirds all of the violent offenses. In a 10-year follow-up study of 10% of the original Philadelphia birth cohort, Wolfgang, Thornberry, and Figlio (1987) found that these chronic offenders had increased the seriousness of their offending into adulthood. In an effort to replicate and extend these research findings, Tracy, Wolfgang, and Figlio (1990) conducted the Second Philadelphia Birth Cohort Study, which was a retrospective study of the official records of more than 27,000 individuals who were born in Philadelphia in 1958 and socialized in the 1960s and 1970s. Although the prevalence of offending in general was similar to that of the first Philadelphia Birth Cohort Study, Tracy et al. found even higher rates of chronic offending among the members of the Second Philadelphia Birth Cohort. More specifically, they found that the chronic offenders represented 7% of the cohort and 23% of the offenders yet were responsible for committing 61% of all the offenses, including 60% of the homicides, 75% of the forcible rapes, 73% of the robberies, and 65% of the aggravated assaults.
The novel and influential findings generated from both the Gluecks’s and Wolfgang et al.’s birth cohort studies stimulated a series of other well-recognized longitudinal studies that have made notable contributions to the criminological literature in recent years. With some exceptions, a number of these studies are relatively recent, and thus not enough time has passed to enable tracking of these individuals into middle/late adulthood. However, there are two such examples of efforts that have been undertaken to follow participants from childhood into middle/late adulthood. Laub and Sampson (2003) are credited with the first of these efforts, wherein they conducted a qualitative and quantitative analysis of a follow-up of the Gluecks’s (1930) study (reviewed earlier) of the criminal careers of the 500 Boston-area male delinquents through age 70. In comparison, Piquero, Farrington, and Blumstein (2007) most recently presented the results of a thorough analysis of the criminal careers of 411 South London males from age 10 to 40 who participated in the Cambridge Study in Delinquent Development (West & Farrington, 1973).
It is important to note that Laub and Sampson’s (2003) follow-up study of the Boston delinquents is the longest longitudinal study of criminal activity in the field. In recognition of this, a series of key findings from their research efforts are worth highlighting. Although the results from a trajectory analysis suggested that there were six groups of individuals who demonstrated unique patterns of involvement in crime over the life course, the trajectory groups for the most part appeared to desist in middle/late adulthood, with virtually no group demonstrating continued involvement in crime at age 70. Although further trajectory analysis results disaggregated by crime type (property, violent, alcohol/drugs) revealed interesting similarities and differences compared with the aggregate trajectory analysis such that property crime trajectories mirrored the aggregate trajectories, violent crime trajectories appeared to peak later, and alcohol/drug trajectories seemed relatively stable throughout young and early/middle adulthood, subsequent attempts to determine key risk/protective factors that distinguished trajectory groups from one another were not fruitful.
Nevertheless, as mentioned earlier, Laub and Sampson (2003) also incorporated a qualitative element into their research in that they conducted extensive interviews with 52 of the delinquent males. On the basis of the individual interviews, it appeared that criminal justice intervention was a risk factor for some and a deterrent for others—in other words, some of the respondents reported that their criminal justice involvement caused them to stop their offending, whereas others indicated that their criminal justice involvement increased/enhanced their continued participation in offending. Another key finding from Laub and Sampson’s interviews of the Gluecks’s (1930) participants was in regard to life transitions. Their qualitative analysis appeared to suggest that marriage was a key source of informal social control, or a turning point, in their lives that caused them to give up their involvement in crime.
As a point of comparison, Piquero et al.’s (2007) research represents the second study that involves longterm follow-up of individuals tracked from childhood into middle/late adulthood. In their analysis, Piquero et al. used data from the Cambridge Study in Delinquent Development (West & Farrington, 1973) to investigate and describe the offending patterns of 411 South London males who were first contacted at the ages of 8 through 10 in the early 1960s for participation in the study. The findings that emerged from Piquero et al.’s efforts were based on the official conviction records of the males at age 40 along with a series of self-reports of their involvement in criminal activity in order to gather information related to the progression of their offending over time.
A series of key findings from Piquero et al.’s (2007) analysis relate to each of the respective dimensions of criminal career research and have import for life course criminology. The first of these results is in regard to the prevalence of offending, the peak age of criminal activity, and the stability/variability of crime over the life course. Piquero et al. revealed that nearly 2 out of every 5 of the South London males (e.g., 40%) accumulated an official conviction for a crime at some point in their lives. However, it appeared that the prevalence of offending for the sample peaked in late adolescence, at approximately age 17. Furthermore, the results indicated that for the most part the frequency of offending tended to follow the prevalence (with violence being the exception) and that there was a considerable degree of stability in offending across age.
The next set of significant research findings germane to criminal career dimensions and life course criminology were onset and frequency and severity of offending, offense specialization, and career length. Regarding the relationship between onset age (the age at which an individual commits his or her first offense) and frequency of offending and severity of offending, Piquero et al. (2007) found that an early onset of offending was related to having a more extensive criminal career as determined by accumulating numerous convictions, having a higher probability of participation in violence, demonstrating a longer criminal career, and displaying involvement in many different types of offenses. Furthermore, there was virtually no evidence of specialization in violence among the offenders from South London. In contrast, the results seem to suggest that involvement in violence was related to offending frequency such that individuals who were committing the greatest number of offenses were also those who were the most likely to have a violence conviction. Thus, violent offenders just tend to roll the dice more often. Turning toward career length, Piquero et al.’s results suggested that the average length of a criminal’s career (measured as the time from first offense to the time at last offense) was 10 years and that there was a general decline in age for both residual career length and residual number of offenses.
The last two key findings from Piquero et al.’s (2007) analysis can be directly compared with the early criminal career research on chronic offenders and chronic offending (e.g., Wolfgang et al.’s [1972, 1987] studies) and Laub and Sampson’s (2003) trajectory analysis with the Gluecks’s (1930) data. Similar to the evidence described earlier in the discussion of Wolfgang et al.’s (1972, 1987) studies, Piquero et al.’s analysis of chronic offenders and chronic offending found that a small group of the males with five or more convictions was responsible for a significant amount of the sample’s total convictions. At the same time, their analysis also indicated that the probability of recidivism after the fourth conviction was very similar there-after, that is, 84.5%. Finally, whereas Laub and Sampson’s trajectory analysis with the Gluecks’s data revealed six trajectory groups through age 70, Piquero et al.’s trajectory analysis of the conviction records among the South London males suggested the presence of five distinct groups of offenders. Despite this difference, like Laub and Sampson’s results, each of the trajectory groups identified in Piquero et al.’s analysis had unique shapes and levels of offending through age 40 and varied on several criminal career dimensions. In addition, Piquero et al. were also able to identify a set of environmental and individual risk factors that were able to distinguish membership in the five distinct trajectory groups.
The Life Course Paradigm
Running in parallel with these criminal careers studies, the fields of sociology and psychology have outlined a life course paradigm. The life course paradigm can be defined as a series of pathways throughout the developmental process in which there are varying age-dependent expectations and available options in an individual’s decision-making process. These decisions, along with the natural course of life events, are seen to shape the trajectory of an individual’s life and can be influenced by transitions and turning points (Elder, 1985). Trajectories are viewed as pathways of development over the life span, such as work life, marriage, schooling, or involvement in crime. They are seen as long-term behavioral patterns that are marked by a sequence of life events and transitions. These transitions are then described as distinct life events that occur in shorter intervals that may alter an individual’s behavioral trajectory (e.g., first job, first marriage, first child; Elder, 1985, pp. 31-32). According to Elder (1985, p. 32), the interlocking nature of trajectories and transitions may generate turning points or changes in the life course.
More recently, Sampson and Laub (1993) extended this framework by focusing on the strong association between childhood events and adulthood experiences and the idea that transitions can redirect an individual’s life course behavioral pathway. They indicated that life course analysis focuses on the length, timing, and the order of significant life events (including crime) and their effect on future social development. Attention to the impact of life events is critical, because research has shown that committing a crime has a considerable behavioral influence on the likelihood of an individual committing crime in the future (for a review, see Nagin & Paternoster, 2000). Furthermore, Sampson and Laub (p. 303) focused on age-graded life transitions and argued that institutions of formal and informal social control matter and vary over the life course. They contended that age-graded informal social control is essential for promoting interpersonal bonds that link individuals to the larger social institutions in which they live (i.e., work, family, school). They also acknowledged that both continuity and within-individual changes do occur over time and that specific life transitions and other factors related to development may intervene in one’s pathway of offending (Farrington, 1986b, referred to this as the stepping-stone approach). Ultimately, the life course paradigm is best summarized as “pathways through the age-differentiated life span,” where age differentiation “is manifested in expectations and options that impinge on decision processes and the course of events that give shape to life stages, transitions, and turning points” (Sampson & Laub 1993, p. 8; see also Elder, 1985).
Life Course Criminology
In recognition of the robust relationship between age and crime, the importance of early influential criminal career research (Glueck & Glueck’s [1930, 1950] and Wolfgang et al.’s [1972, 1987] studies) and the findings generated from recent efforts (Farrington, 2003; Blumstein et al., 1986; Laub & Sampson, 2003; Piquero et al., 2007), and appreciating the life course paradigm developed in sociology and psychology, there has emerged a subfield within criminology known as DLC criminology (Farrington, 2003).
Within criminology, the life course perspective is an effort to offer a comprehensive outlook to the study of criminal activity because it considers the multitude of factors that affect offending across different time periods and contexts (Thornberry, 1997). One of the core assumptions of DLC theory is that changes with age and delinquency and criminal activity occur in an orderly way (Thornberry, 1997, p. 1), and some of the DLC theories that have begun to emerge from this perspective have in large part made an effort to not only document crime over the life course but also to more readily identify the key risk and protective factors associated with the onset, persistence, and desistance from criminal activity. Furthermore, these DLC theories have made efforts to integrate knowledge from other disciplines outside of criminology into their theoretical frameworks, most notably drawing from psychology, sociology, biology, and public health.
In general, DLC theory concentrates on three main issues: (1) the development of offending and antisocial behavior, (2) the effect of risk and protective factors at different ages on criminal activity at different ages, and (3) the effects of life events on the course of development and criminal activity throughout the life course (Farrington, 2003, p. 221). With regard to the first issue, empirical research has documented the progression of delinquency and criminal involvement over time (see, e.g., Tracy et al., 1990), but there is a general lack of available data that follows individuals from early on in life well into middle and/or late adulthood (for important exceptions, see Laub & Sampson, 2003; see also Piquero et al., 2007). Concerning the second issue, research is beginning to identify key risk and protective factors that have an impact on whether an individual becomes involved in crime in the first place and whether he or she continues to be involved in crime over the life course (see Hawkins & Catalano, 1992; Loeber & Farrington, 1998). Turning toward the final issue (as identified by Farrington, 2003), recent research evidence has suggested that several key life events, such as marriage and steady employment, not only appear to be related to participation in offending but also seem to be particularly important in the reduction of criminal activity and fostering desistance from crime in general (Farrington & West, 1993; Horney, Osgood, & Marshall, 1995; Laub, Nagin, & Sampson, 1998; Piquero, Brame, Mazzerole, & Haapanen, 2002). In contrast, additional research has shown that other life events, such as incarceration, are a risk factor for subsequent and continued involvement in criminal activity (Sampson & Laub, 1997).
In his review of DLC theory and research, Farrington (2003, pp. 223-224) identified 10 widely accepted conclusions about the development of criminal offending:
- The prevalence of offending peaks in the late teenage years.
- The peak age of onset of offending is between 8 and 14, and the peak age of desistance from offending is between 20 and 29.
- An early age of onset predicts a relatively long criminal career duration.
- There is marked continuity in offending and antisocial behavior from childhood to the teenage years and to adulthood.
- A small fraction of the population (the chronic offenders) commits a large fraction of all crimes.
- Offending is versatile rather than specialized.
- The types of acts defined as offenses are elements of a larger syndrome of antisocial behavior.
- Most offenses up to the late teenage years are committed with others, whereas most offenses from age 20 onward are committed alone.
- The reasons given for offending up to the late teenage years are quite variable, including utilitarian reasons, for excitement or enjoyment, or because people get angry.
- Different types of offenses tend to be first committed at distinctively different ages.
Considering this list of relatively undisputed truths about the development of criminal offending, it is also important to point out that the strength of the evidence for these truths does range considerably from relatively strong evidence to substantially strong evidence. Keeping this in mind, Farrington (2003, pp. 225-227) also described a series of issues in DLC criminology that are still points of contention to which DLC theories and research should attend. For instance, although the evidence is fairly robust with regard to the prevalence of offending peaking during late adolescence, the research is not as clear as to how an individual’s frequency of offending fluctuates in any given year and whether seriousness escalates and de-escalates as a function of age. Furthermore, two related issues concern the relationship of early-onset offending with later-onset offending and chronic offending with less frequent offending. More specifically, it is not yet determined whether early-onset offenders are different in degree or kind from late-onset offenders or whether chronic offenders are merely distinguishable from less frequent offenders in the number of offenses committed or if their offense repertoires are in fact distinct from one another.
The last few contentious DLC issues (identified by Farrington, 2003) focus on escalation, risk and protective factors, and intermittency in criminal careers. First, the research is not clear on whether certain types of offenses act as precursor events or gateway offenses (or stepping stones) for other types of offenses. For instance, does burglary lead to later sexual offending? Second, although risk and protective factors for early-onset offending are well-known, the evidence is lacking on whether these factors are in fact causal or whether they are merely indicators of the same underlying construct. Finally, research should incorporate and seek to explain the possibility that intermittency in criminal careers affects their results. For example, all offenders do not necessarily start offending at one particular point in time, continue offending for some duration, completely quit (desist) at another particular point in time, and never offend again. Instead, some offenders appear to desist for some period of time before restarting some years later, perhaps in response to some adverse life event such as losing a job, getting a divorce, or developing a substance abuse problem.
Acknowledging the current truths and points of contention in DLC research, the following section of this chapter highlights some of the key DLC theories and reviews their basic assumptions and expectations. The chapter concludes by offering some suggestions on where DLC theoretical development and modification and DLC empirical research should perhaps move toward in the future.
Developmental/Life Course Theory
As discussed in the previous section, criminology has witnessed a considerable degree of knowledge infused into its theorizing from other social science and related disciplines. This recent growth in interdisciplinary thought has likely had the largest effect on the origins of DLC theories. The following discussion reviews of some of criminology’s most recognizable DLC theories, with particular attention paid to those that have received a considerable amount of empirical research.
Similar to Moffitt’s (1993) developmental taxonomy, Patterson and Yoerger’s (1999) theory is also based on a two-group offending model: early-onset offenders and late-onset offenders. As Patterson and Yoerger discussed, poor and inept parenting practices lead to ineffective early childhood socialization, which allows for the development of oppositional/defiant behavior and early-onset offending. Furthermore, this ineffective socialization also causes these youth to be involved with deviant peers, which thereby magnifies their probability and intensity of offending. Patterson and Yoerger went on to suggest that early-onset offenders tend to be aggressive and defiant in their interactions with others and come to be rejected by conventional peers. Thus, these early-onset offenders tend to “find” one another and thereby form their own deviant peer groups, which places them at a high risk for chronic offending and continued offending over the life course.
In contrast, Patterson and Yoerger (1999) suggested that the late-onset offender group is not composed of individuals who suffer from poor and ineffective socialization; instead, the main cause of their offending is their interaction with deviant peers. Considering that the peer social context of adolescence is one of general support/acceptance for deviance, these late-onset offenders engage in delinquency during middle to late adolescence. However, because these youth did not enter into this developmental period suffering from ineffective childhood socialization they are able to confine their offending to this development period and go on to lead prosocial and productive adult lives. Several empirical studies have tested this theory and for the most part have supported the underlying assumptions of Patterson and Yoerger’s theory (see Simons, Johnson, Conger, & Elder, 1998; Simons, Wu, Conger, & Lorenz, 1994).
Loeber and his colleagues (Loeber, Farrington, Stouthamer-Loeber, Moffitt, & Caspi, 1998; Loeber, Wei, Stouthamer-Loeber, Huizinga, & Thornberry, 1999) have proposed a three-pathway model for describing the developmental progression of chronic offending. The first, the overt pathway, is believed to begin with minor acts of aggression, followed by physical fighting that ultimately escalates to violence. The second pathway, called the covert pathway, consists of a sequence of minor deviant behaviors followed by property damage and then escalates to more serious types of offending. The final pathway, the authority-conflict pathway, observed before age 12, consists of a sequence of stubborn behaviors, including defiance and authority avoidance (e.g., running away). Although according to Loeber et al.’s theoretical model individuals’ developmental progression of delinquency can cross over the three pathways, the most frequent offenders are expected to be overrepresented among those in multiple pathways, particularly youth who exhibit overt and covert behavior problems.
With attention to the three pathways just described, it is important to mention that a key assumption of Loeber et al.’s (1998, 1999) theoretical model is that behavior takes place in an orderly, not random, fashion. Stated differently, an individual’s pathway of offending is expected to progress through the lower-order steps before passing through the higher-order steps. Preliminary support for Loeber et al.’s pathway model was identified in the youngest sample of the Pittsburgh Youth Study and applied better to boys who persisted in delinquency compared with those who experimented in delinquency (Loeber et al., 1998). Furthermore, more recent replications of the pathway model have been provided in the three “Causes and Correlates Study” sites (Denver, Colorado; Pittsburgh, Pennsylvania; and Rochester, New York), although the findings were replicated only for Steps 2 and higher in the overt and covert pathways only (Loeber et al., 1999; although see Nagin & Tremblay, 1999).
One last DLC theory reviewed in this chapter is that of Sampson and Laub’s (1993) age-graded theory of informal social control. This theory can best be described with attention to what Sampson and Laub characterized as a series of building blocks. The first building block focuses on the intervening role of informal family and school social bonds. The second building block focuses on the continuity of antisocial behavior that begins early in a child’s development and extends throughout adulthood. They also recognized that particular life events and social ties in adulthood can alter an individual’s behavioral trajectory, and this viewpoint is central to their third building block: the importance of adult social bonds. They proposed that social bonds developed in adulthood (employment, marriage) can explain involvement/lack of involvement in crime regardless of any underlying individual criminal propensity. In addition, they emphasized that it is not only the mere exposure of individuals to these bonds that is critical but also the quality and intensity of these bonds. Drawing on the work of Elder (1985), Sampson and Laub also hypothesized that different adaptations to key life events can affect an individual’s trajectory, and crucial turning points such as divorce or death of a loved one can redirect life trajectories.
In comparison, cumulative continuity (Moffitt, 1993) integrated with the concept of state dependence (for a review, see Nagin & Paternoster, 2000) refers to the idea that involvement in delinquency has an incremental effect on the interpersonal social bonds formed in adulthood (i.e., labor force attachment, marital cohesion). For instance, an arrest and subsequent incarceration in adolescence may lead the youth to drop out of school. This practice would logically affect his future job prospects and thus result in his failure to develop strong adulthood bonds to the labor force, which inevitably increases the likelihood of his involvement in crime (Tittle, 1988).
It is important to mention here that Sampson and Laub (1997) extended their age-graded theory of informal social control to incorporate a developmental conceptualization of labeling theory. Sampson and Laub suggested that involvement in delinquency has a “systematic attenuating effect on the social and institutional bonds linking adults to society (e.g., labor force attachment, marital cohesion)” (p. 144). Therefore, the relationship between delinquency and future criminal involvement is indirect in that delinquent participation leads to school failure, incarceration, and the development of weak bonds to the labor market, of which all of these factors are significantly associated with future criminal activity. Furthermore, for Sampson and Laub, this cycle occurs because severe sanctions label and stigmatize offenders, which thereby limits offenders’ opportunity for involvement in a conventional lifestyle and participation in mechanisms of informal social control (e.g., legitimate employment). One early test of this theoretical model did in fact provide some preliminary support for Sampson and Laub’s assumptions in that, compared with delinquents with a shorter incarceration history, boys who were incarcerated for a longer time had trouble securing stable jobs as they entered young adulthood (Sampson & Laub, 1997).
Although the DLC theories just reviewed are distinct from one another, they certainly share some common theoretical ground. Having said this, there is a clear divide. For example, Sampson and Laub’s (1997) theory is dynamic general theory but allows for the possibility that key local life circumstances can alter an individual’s criminal trajectory. In comparison, DLC theories such as Moffitt’s (1993), Patterson and Yoerger (1999), and Loeber et al.’s (1998, 1999) assume not that causality is general but rather that there are different causal processes that explain different offender types. Furthermore, Moffitt’s adolescent-limited offender and Patterson and Yoerger’s late-onset offender typologies are described as a state-dependent effect, whereas the causes of their life-course-persistent offender and early-onset offender counterpart typologies appear to emphasize persistent heterogeneity. Nevertheless, although this difference is important, most of the research has tended to favor taking the theoretical middle ground when studying crime (see Paternoster, Dean, Piquero, Mazerolle, & Brame, 1997), which suggests that explanations of persistent heterogeneity and state dependence are not necessarily incompatible or mutually inconsistent at all times.
Conclusion: Research Needs and Future Directions
On the basis of a review of the evidence, and with attention to the specific DLC theories covered in this chapter, it appears that there are many more questions than answers from this growing area of research and theorizing. This final section highlights several important research needs and anticipates several future directions for research on DLC criminology.
For instance, although DLC theories tend to express assumptions that have borrowed from research evidence across an array of disciplines, such as biology, public health, and the social sciences in general, there have not been many attempts to test these theories across the disciplines and/or involving cross-disciplinary collaborations among researchers in prior empirical tests. Second, recognizing that this is a relatively new area of criminological research, there have not been many attempts to date to incorporate multilevel models into tests of DLC theories. Studies such as these are likely to be highly beneficial to DLC research, because a number of these theories discuss risk and protective factors that are multilevel in nature (e.g., the importance of the school environment and residing in a disadvantaged neighborhood). Future research should attempt to collect and/or make use of macrolevel risk and protective factors when available and model these effects both independently and simultaneously alongside the individual-level risk and protective factors when empirically assessing DLC theories.
Another underdeveloped area of DLC research is an exploration of how many offender groups there may be. Although certain DLC theories suggest two offender groups (Moffitt, 1993; Patterson & Yoerger, 1999) and others discuss multiple pathways (Loeber et al., 1998, 1999), results from more than 80 studies using trajectory analysis have suggested between three to five offender groups (for a review, see Piquero, 2008). Some of these groups are consistent with notable DLC theories (e.g., adolescent-limited offenders and life-course-persistent offenders), whereas other groups that are not consistent with some DLC typologies, such as low-level chronic offenders and late-onset offenders (who do not begin their offending until adulthood) have also emerged from this research. Future DLC studies should continue their efforts at replicating prior trajectory-analysis-based research in attempt to shed more light on the consistencies regarding the number of offender groups as well as incorporating risk and protective factors in their research to determine what covariates are significant for distinguishing trajectory group membership.
Last, DLC theories and related empirical research in the future should devote specific attention to race and gender. For the most part, the current DLC theories are relatively quiet on how race and gender may matter, or at the very least there have been only a handful of studies testing the generalizability of these theories across race and gender. Furthermore, a lot of the existing research in this area (similar to criminological research in general) relies either on self-report or official data. Although the limitations of both sources are well-known to criminologists, future DLC research should recognize this issue and attempt, when possible, to use some sort of a triangulation of methods to provide a more definitive conclusion on the progression of delinquency and criminal involvement over the life course. Thus, it is indeed an exciting time to be involved in DLC criminology, and as the subfield moves forward, those interested in this area of research may benefit from the suggestions given in this chapter as they become involved or continue their involvement with DLC criminological theory development and modification and/or empirical testing. This chapter closes by providing the reader with Farrington’s (2003, pp. 229-230) excellent list of the key empirical and theoretical issues that need to be addressed by any DLC theory:
- Why do people start offending?
- How are onset sequences explained?
- Why is there continuity in offending from adolescence to adulthood?
- Why do people stop offending?
- Why does prevalence peak in the teenage years?
- Why does an early onset predict a long criminal career?
- Why is there versatility in offending and antisocial behavior?
- Why does co-offending decrease from adolescence to adulthood?
- Why are there between-individual differences in offending?
- What are the key risk factors for onset and desistance, and how can they be explained?
- Why are there long-term (over life) and short-term (over time and place) within-individual differences in offending?
- What are the main motives and reasons for offending?
- What are the effects of life events on offending?