Broadly, longitudinal research is research that involves longitudinal data, that is, data with a time dimension. This can be contrasted with cross-sectional data, which records information about the units of analysis at a particular point in time. Longitudinal research in criminology can be used for a variety of purposes, including quantifying trends in human behavior over time, describing the progression of life events, identifying patterns of behavior change, testing theories of crime causation, and evaluating the impact of interventions including criminal justice policy. Different types of longitudinal studies can be used for each of these aims. Panel studies look at multiple waves of data collection using same measures and sample. Cohort studies involve a particular group of individuals that are studied over time, such as a “birth cohort” or a “prison cohort.” Time-series studies involve a series of measurements taken at periodic time intervals in order to measure the impact of a change (such as a policy intervention) by comparing before- and after- measurements of the phenomena of interest. Trend studies look at change over time in a total population or sample that is generalizable to that population. In what follows, longitudinal research in criminology is reviewed with an emphasis on prospective cohort designs. First, an overview of longitudinal research and the methods for analyzing longitudinal data is first provided. Next, major longitudinal cohort studies are discussed, including early (pre-1970) and later (post-1970) cohort studies, long-term follow-ups of prospective cohort studies, and major longitudinal-experimental designs. These studies have allowed researchers to control for possible cohort effects, i.e., similarities within the group, when examining patterns in offending over time. This is especially useful for “life course” researchers who are interested in how a sequence of socially defined events affects individuals over time (i.e., age and period effects). Applications of longitudinal research are then discussed. Most notably, this involves developmental and life-course criminology, which requires longitudinal research to examine criminal careers, early risk factors for offending, offending trajectories, and adult transitions and desistance. Additionally, longitudinal research has been utilized to examine intergenerational transmission of crime, to test major theories of crime, to assess the impact of criminal justice policy, and to examine aggregate trends in crime and punishment. Each of these is briefly discussed.
Life-Course Criminal Trajectories of Mafia Members