Group-based trajectory models are used to investigate population differences in the developmental courses of behaviors or outcomes. This note introduces a new Stata command, traj, for fitting to longitudinal data finite (discrete) mixture models designed to identify clusters of individuals following similar progressions of some behavior or outcome over age or time. Normal, Censored normal, Poisson, Zero-inflated Poisson, and Logistic distributions are supported.
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JonesB. L.NaginD. S.RoederK.2001. “A SAS Procedure Based on Mixture Models for Estimating Developmental Trajectories.”Sociological Methods & Research29:374–93.
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LacourseR.CôteS.NaginD. S.VitaroF.BrendgenM.TremblayR. E.2002. “A Longitudinal-experimental Approach to Testing Theories of Antisocial Behavior Development.”Development and Psychopathology14:909–24.
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NaginD.2005. Group-based Modeling of Development. Cambridge, MA: Harvard University Press.
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NaginD.OdgersC. L.2010. “Group-based Trajectory Modeling in Clinical Research.”Annual Review of Clinical Psychology6:109–38.
