Statistics is the field of knowledge concerned with data collection, data analysis, and data interpretation and presentation. Methodology comprises the many and varied structured ways in which research is conducted answering the fundamental question: How does the researcher effectively gather information for particular purposes? Both are core topics underlying the discipline of psychology and the other social, behavioral, and health sciences. Moreover, a basic understanding of the language of statistics and research methods is required for any serious student, scientist, and practitioner in these fields. The APA Dictionary of Statistics and Research Methods is a focused reference resource that explores the lexicon of these two tightly interrelated areas. It provides Over 4,000 entries offering clear and authoritative definitions; Balanced coverage in such core areas as research planning and design, psychometrics, quantitative and qualitative measurements, and data analysis; Hundreds of incisive cross-references that deepen the user's understanding of related topics; More than 100 illustrations of some of the common and uncommon data display methods; A Quick Guide to Use that explains stylistic and formal features at a glance; and Appendixes listing common abbreviations and statistical symbols The largest scientific and professional organization of psychologists in the United States and the largest association of psychologists in the world the American Psychological Association proudly offers this reference as part of its critically acclaimed APA Dictionaries series.