Public Health: Epidemiology

Core functions of epidemiology include:

• public health surveillance -- the ongoing, systematic collection, analysis, interpretation, and dissemination of public health data
• field investigation -- may be as simple as a phone call or as complex as a multi-agency response to an event
• analytic studies -- evaluate the hypotheses from surveillance and field work
• evaluation -- the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals
• linkages -- maintain relationships and share information with staff of other agencies and institutions
• policy development -- regularly provide input, testimony, and recommendations regarding disease control strategies, reportable disease regulations, and health care policy

Clinical epidemiology is the science of making predictions about individual patients by counting clinical events (the five Ds) in groups of similar patients and using strong scientific methods to ensure that the predictions are right.  In the clinical setting, epidemiological methods are used to make a prediction about a health outcome for an individual based on scientific studies of groups of similar patients.  Clinical epidemiology is integral to evidence-based medicine.

Descriptive epidemiology identifies patterns among cases and in populations, by time, place, and person.  From these observations, epidemiologists develop hypotheses about the causes of the patterns and the factors that increase the risk of disease. 

Analytical epidemiology deals with the search for causes and effects, or the why and the how.  Epidemiologists use analytic epidemiology to quantify the association between exposures and outcomes and to test hypotheses about causal relationships.  Analytical studies address the "why" and "how" as opposed to the "person/place/time" of descriptive studies.   The hallmark of an analytical epidemiological study is the use of a valid comparison group.

Prevalence is the number of existing cases in the bubble during a certain time period. Prevalence is a measure of disease burden.

Incidence is the number of new cases entering the bubble during a certain time period.  Deaths and cures are the cases leaving the bubble.Incidence is a measure of disease risk.

Point prevalence is the number of cases at a single point in time while period prevalence is the number of cases over a specific period of time. In general, one month is used for short lived things like the flu while at least six months is used for chronic conditions. 

Duration is the length of time a condition usually lasts.

PREVALENCE = INCIDENCE x DURATION