Advances in Clinical Child Psychology is a serial publication designed to provide researchers and clinicians with a medium for discussing new and innovative approaches to the problems of children. In this fourth volume, a group of highly distinguished authors have described advanc ing knowledge in a number of critical areas of applied child psychology. These include childhood depression, drug abuse, social skills deficits, community-living skills, the genetics of childhood behavior disorders, and affective states in children. In addition, major statements on new approaches to the assessment of dysfunctional family systems and the social skills of children, as well as the increasingly important methodol ogy of epidemiology, are included in this volume. These chapters pro vide a synopsis of many of the most important advances in the field of clinical child psychology. The quality of a series of this sort is, of course, due to the quality of the contributing authors. We feel very fortunate indeed, therefore, to have been able to entice such a distinguished group of authors to con tribute to this volume. We are also most appreciative of the guidance and assistance of the consulting editors who provided us with ideas for chapter topics and authors and who carefully reviewed and edited each chapter. We also express our hearty thanks to Leonard R. Pace of Plenum whose expertise and support has always been generously given. BENJAMIN B. LAHEY ALAN E. KAZDIN ix Contents The Epidemiology of Child Psychopathology 1 William Yule 1. Introduction ............................................ .