Group based trajectory modeling (GBTM) was used to characterize the development of auditory P300 amplitude over the ages of 8 through 29 and to investigate the possible association of P300 developmental trajectory with familial risk for alcohol dependence. Analyses were conducted using SAS PROC TRAJ (Jones et al., 2001; Jones and Nagin, 2007) using a semi-parametric group-based approach for modeling of developmental trajectories. GBTM provides a flexible method for identifying clusters of individual trajectories following a similar developmental path and characterizing individuals within those clusters. The group-based approach uses a discrete distribution and multinomial model to characterize population heterogeneity in development. The multinomial model allows for the estimation and testing of potential covariate associations with group membership. This semi-parametric approach contrasts with hierarchical and latent curve methodologies that model population variability in development with continuous distributions.
