The third edition of this resource is intended to assist students and professionals in increasing their mastery of the range of methodological approaches available with which to examine clinical issues and phenomena. Contributors explore experimental design; the principles, procedures and practices that govern research; assessment of study constructs and their interrelationships; potential sources of artifact and bias; methods of data analysis and interpretation; ethical issues; and publication and communication of research findings. With 19 new articles and significantly revised and expanded introductory material, this edition features many scholarly contributions that explicate core concepts, survey contemporary issues, and elaborate on ethical responsibilities. Additions include articles on mediators and moderators of effects, on methods for studying the efficacy and effectiveness of psychotherapy, and on ways of incorporating systematic observation and evaluation into clinical practice to improve patient care.