Epidemiology is the study of the distribution and determinants of health-states or events in specified populations, and the application of this study to the control of health problems.

Reference: Last, JM. Dictionary of Epidemiology. UK, 1988

Epidemiological information, particularly that defining individual, population and/or physical environmental risks has been at the core of public health, and provided the basis for disease prevention activities. Epidemiological studies use social classifications (such as socioeconomic status) in the study of disease in populations, but generally make less than optimal use of social sciences, including economic and public policy information, in investigating and understanding disease and health in populations.

Social epidemiology has evolved as a discipline during the past two decades. Social epidemiology is the study of health and illness in populations which is informed by a social, psychological, economic and public policy information, and uses that information in the definition of public health problems and proposal of solutions. As the discipline of epidemiology further develops and expands such distinctions will be less important in the future.

Source: Health Promotion Glossary (1998), WHO/HPR/HEP/98.1