A developmental trajectory describes the course of a behavior over age or time. This three-day workshop aims to provide participants with the training to apply a semiparametric, group-based method for analyzing developmental trajectories described in Nagin's "Psychological Methods" article (1999, 4:139-157). This methodology has four significant capabilities to:
- identify rather than assume distinctive groups of trajectories
- estimate the proportion of the population following each such trajectory group
- relate group membership probability to individual characteristics and circumstances
- use the group membership probabilities for various other purposes, such as creating profiles of group members
In addition, workshop participants will be trained in the application of two important extensions of the method--the capabilities to add time-varying covariates to trajectory models and estimate joint trajectory models of distinct but related behaviors. The former provides the statistical capacity for testing whether a contemporaneous factor, such as an experimental intervention or a nonexperimental event like pregnancy, deflects a preexisting trajectory. This extension is intended to provide the statistical capacity for modeling turning points in the context of a group-based trajectory model. The latter extension provides the capability to study the unfolding of distinct but related behaviors, such as childhood problem behavior and adolescent drug abuse. This extension is designed to address two prominent themes in developmental psychology and criminology--comorbidity and heterotypic continuity. Comorbidity refers to the contemporaneous occurrence of two or more undesirable conditions, such as conduct disorder and hyperactivity. Heterotypic continuity is the manifestation over time of a latent individual trait in different but analogous behaviors.
Workshop participants will also receive training in the application of the Wald test for determining whether differences in model parameters across trajectory groups are significantly different, and in using the parametric bootstrap for computing confidence intervals for quantities such as the probability of trajectory group membership for individuals with specified characteristics.
The workshop will combine lectures with hands-on, computer lab experience in estimating, analyzing, and interpreting trajectory models. Specifically, participants will be trained in the use of an SAS-based procedure for estimating group-based trajectories. This procedure, called TRAJ, has the capacity to fit models to psychometric, count, and binary longitudinal data. The training will involve the application of TRAJ to masked data extracted from a major longitudinal study. Participants may bring their own data sets to analyze in the computer lab, but the primary focus will be on supporting participants who are working on the designed training exercises.
Daniel S. Nagin received his doctoral degree in 1976 from the school now known as the Heinz School of Public Policy and Management, at Carnegie Mellon University, where he is now the Teresa and H. John Heinz III Professor of Public Policy. His research focuses on the evolution of criminal and antisocial behaviors over the life course; the deterrent effect of criminal and noncriminal penalties on illegal behaviors; and the development of statistical methods for analyzing longitudinal data. His work has appeared in such diverse outlets as The American Economic Review, American Sociological Review, Journal of the American Statistical Association, American Journal of Sociology, Archives of General Psychiatry, Criminology, Child Development, Psychological Methods, Law & Society Review, Crime and Justice Annual Review, Operations Research, and Stanford Law Review.
Nagin is the author of the forthcoming book Group-based Modeling of Development, to be published by Harvard University Press. He is a member of the MacArthur Network on Social Interactions and Economic Outcomes, the MacArthur Network on Adolescent Development and Juvenile Justice, and the National Research Council's Committee on Law and Justice. He also serves on the steering committee of the National Consortium on Violence Research and on numerous editorial and advisory boards. From 1981 to 1986 he was deputy secretary of fiscal policy and analysis in the Pennsylvania Department of Revenue. Professor Nagin has served on the boards of directors of the Pennsylvania Energy Development Authority and the Pittsburgh Filmmakers. He is a Fellow of the American Society of Criminology and the American Association for the Advancement of Science, and a 1985 recipient of the Northeastern Association of Tax Administrators Award for Excellence in Tax Administration.