Criminology Trajectory Methods in Criminology
by
Wesley G. Jennings, Alex R. Piquero
  • LAST MODIFIED: 23 May 2012
  • DOI: 10.1093/obo/9780195396607-0070

Introduction

Trajectory modeling has recently come into favor in criminological research. Advances in methodology and statistics have provided the opportunity for criminologists to study, document, and understand developmental trajectories of criminal activity and behavior. Through the use of longitudinal data, criminologists can study behavioral change and the change in patterns of criminal activity over the life course, with such inquiries as: Are there certain trajectories of offending that begin early, continue through adolescence, and persist into adulthood? Are there certain offending trajectories that can be considered late onset? Are there certain risk and protective factors that differentially predict which trajectory an individual’s offending pattern may follow? And, do these offending trajectories generalize across biological sex, race, ethnicity, social class, time, and geographic location? Numerous longitudinal studies have been conducted throughout the world, examining these various research questions. The use of longitudinal data and trajectory models has provided criminologists with rich data to analyze research questions that would not have been possible to address through cross-sectional research. Historically, several findings exist that are common to longitudinal studies: misbehavior starts early in life and is often identifiable early, but not always. The majority of longitudinal studies have charted persistence of criminal behavior effectively, but they have not been as successful in charting desistance. Longitudinal studies have, for the most part, found the correlates of persistence and desistance of delinquent behavior to be dissimilar and not necessarily indicative of factors that contribute to early onset. And advances in statistical tools have allowed researchers to examine behavioral patterns of criminal activity more directly. A comprehensive examination of the various trajectory studies that have been conducted recently by sample type and time period as well as a summary of the key findings from these various trajectory studies will give further insight into what the field of criminology has learned from this trajectory methodology. Some of the key information discovered from applications of the trajectory methodology in criminology includes determining that adolescent-limited and life-course-persistent trajectory patterns can be identified. On average, three to five trajectory groups are identifiable using the trajectory methodology, and the relative number of trajectory groups often varies as a function of sample size. There are a variety of directions that can be taken in regard to longitudinal research and the trajectory methodology to improve the extant knowledge base in the field of criminology. For example, there is a need to further disaggregate the general offending trajectories across sex, race, ethnicity, and cultural contexts. Also, more literature is needed on the identification of multiple risk and protective factor domains such as family, peers, and community context that may serve as important mechanisms for differentiating offender trajectories. Finally, it is important for future criminological research using the trajectory methodology to extend the observation period across multiple developmental periods when data permit, in order to more fully capture the development of offending over the life course.

Theoretical Backdrop

There has been a considerable history of empirical attention directed toward understanding the age-crime curve. This research led to the development of the criminal career paradigm, which focuses on a variety of criminal career dimensions such as participation, frequency, seriousness, specialization, versatility, onset, and desistance. Informed by these criminal career dimensions, life-course/developmental criminology has begun to recently emerge in an attempt to explain why offending varies over time and to identify certain risk and protective factors that can distinguish certain criminal career trajectories from others. Nagin and Land 1993 deals with one of the core issues in criminology, in the authors’ exploration and discussion of the age-crime curve at the individual level. Three issues are addressed within the context of their research: Is the life course of individual offending marked by periods of quiescence? At the individual level, do offending rates vary systematically with age? And are chronic offenders different from less active offenders? Sampson and Laub 2003 takes issue with the typical predictions of group behavior from trajectory modeling, arguing that in essence group-based modeling is unpredictable at best, because groups that do not exist are often reified, and that all offenders, even those with the highest rate of offending, eventually desist from criminal behavior.

  • Nagin, Daniel, and Kenneth Land. 1993. Age, criminal careers, and population heterogeneity: Specification and estimation of a nonparametric, mixed Poisson model. Criminology 31.3: 327–361.

    DOI: 10.1111/j.1745-9125.1993.tb01133.xE-mail Citation »

    Looks at career offending patterns as they relate to the age-crime curve. Asking questions regarding whether offenders differ systematically, the article discusses the use of a mixed Poisson model to analyze a panel set of data tracking males over time. This article is best suited for an audience with elementary-level knowledge of advanced statistical modeling procedures.

  • Sampson, Robert, and John Laub. 2003. Life course desisters? Trajectories of crime among delinquent boys followed to age 70. Criminology 41.3: 555–592.

    DOI: 10.1111/j.1745-9125.2003.tb00997.xE-mail Citation »

    Analyzes data collected from one of the longest longitudinal crime studies to date, of boys and men between the ages of seven and seventy. The authors assess whether distinct offender groups exist or whether individual differences can foreshadow long-term offending trajectories. This is a hallmark piece in criminological research that should be read and reviewed by everyone with an interest in the topic.

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