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It is difficult for epidemiologists to agree on one single definition of the field but a frequently cited definition describes epidemiology as the "study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control of health problems." (Last, 1995).

  • Study—Epidemiology is the basic science of public health. It is a highly quantitative discipline based on principles of statistics and research methodologies.
  • Distribution—Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population. To do this, they use descriptive epidemiology, which characterizes health events in terms of time, place, and person.
  • Determinants—Epidemiologists also attempt to search for causes or factors that are associated with increased risk or probability of disease. This type of epidemiology, where we move from questions of "who," "what," "where," and "when" and start trying to answer "how" and "why," is referred to as analytical epidemiology.
  • Health—related states—Although infectious diseases were clearly the focus of much of the early epidemiological work, this is no longer true. Epidemiology as it is practiced today is applied to the whole spectrum of health-related events, which includes chronic disease, environmental problems, behavioral problems, and injuries in addition to infectious disease.
  • Populations—One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients.
  • Control—Finally, although epidemiology can be used simply as an analytical tool for studying diseases and their determinants, it serves a more active role. Epidemiological data steers public health decision making and aids in developing and evaluating interventions to control and prevent health problems. This is the primary function of applied, or field, epidemiology.
    In other words, epidemiology is the study of our collective health as a community. Epidemiology offers insight into why disease and injury afflict some people more than others, and why they occur more frequently in some locations and times than in others — knowledge necessary for finding the most effective ways to prevent and treat health problems.

Borrowed from the following resource:

John M. Last, ed., A Dictionary of Epidemiology, 3d ed. (New York: Oxford University Press, 1995)

The following links can provide more detailed descriptions of this unique field: