Dictionary making never ends because languages are always changing. Widely used throughout the world, this book will continue to serve as the standard English-language dictionary of epidemiology in its Fourth Edition. It covers all the common terms used in epidemiology and many from related fields such as biostatistics, infectious disease control, health promotion, genetics, clinical epidemiology, health economics, and medical ethics. The definitions are clear and concise, but there is space for some brief essays and discussions of the provenance of important terms. Sponsored by the International Epidemiological Association, the dictionary represents the consensus of epidemiologists in many different countries. All the definitions were reviewed repeatedly by an international network of contributors from every major branch of epidemiology. They are authoritative without being authoritarian. The Fourth Edition contains well over 150 new entries and substantial revisions of about the same number of definitions, plus a dozen new illustrations. Many of the new terms relate to methods used in enviromental and clinical epidemiology.