The measurement of psychiatric symptoms and the subsequent diagnosis of disorders via DSM criteria may not be the optimal system for either clinical or research purposes. This project will develop and apply an array of methods to examine the empirical basis for the DSM nosological system and will develop more efficient methods of analysis of the available data. Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University has assembled a large array of data collected from twins and other family members using state of the art interview schedules for the assessment of psychopathology. The datasets include the Virginia Twin Study of Adolescent Behavioral Development (VTSABD) -- a study of 8-16 year old twin pairs and their parents; the Adult Virginia Twin Studies (AVTS), and studies of adult twins and their parents, both of which contain longitudinal and multiple rater components. In addition, data from an epidemiologic study of juveniles, the Great Smokey Mountains Study (GSMS), and from adults, the National Comorbidity Survey (NCS) will be available for parallel analyses through collaboration with consultants. Existing methods that will be applied to these data include latent class analysis, item response theory, multiple rater models and modern regression methods. Extensions of these methods will be developed and applied, particularly multiple rater models for longitudinal data, multivariate contingent causal models for ordinal data, and structured versions of latent class and item response models that are suitable for the analysis of data collected from families or other clustered groups. Gender differences in symptom expression and subsequent development of clinical disorders will be assessed. Derived classes and trait scores will be validated in four main ways: covariance with risk factors; prediction of outcome over time; familial resemblance; and treatment response in clinical samples available at VCU, The long term goals of the project are to improve the efficiency of measurement, nosology, and knowledge of the etiology of common psychiatric disorders and their comorbidity.