Glossary of Common Epidemiology Terms

Acute disease—a short-term illness, whether mild or fatal. A cold is an acute disease, as is influenza.

Association—when one characteristic is related to another and they change predictably together.

Bias—the amount we are off from the true value. How wrong we are when we don’t get it right.

Biostatistics—the theory and techniques for describing, analyzing, and interpreting health data.

Case—a person in a study who has the particular disease or condition that is being studied.

Cause—a factor or event that produces a second event. In public health, a factor that increases the probability of developing a disease; smoking, for example, causes lung cancer.

Chronic disease—a disease that lasts a long time; often has many causes.

Cohort—a group of people that may share a common characteristic (i.e., they live in a certain town or were born in a certain year) and who are enrolled in a study. The group have their health status followed for a period of time.

Control— a person or group used for comparison. In a trial (experiment), the control group does not receive the drug or agent being tested.

Data—the information collected during a scientific study.

Disease—a term of health status; when something is wrong with a bodily function

Disease cluster—a series of disease cases closely grouped in a specific geographical area or over a specific period of time.

Endemic—the usual existence of an infectious disease in certain areas. For example, malaria is native, or endemic, in southern India because it always infects the mosquitoes of southern India and can be transmitted to people.

Epidemic—any unusual occurrence of disease, generally first noticed by an unexpected number of cases occurring over a particular amount of time or in a particular place. An outbreak of disease, infections or injuries within a defined geographic area or over a specific period of time.

Epidemiology—the use of medical science and statistics to track population health and to find causes of diseases in groups of people.

Exposure—an external factor that may affect health. Cigarette smoking is a well-studied exposure.

Health—a state of complete physical, mental, and social well-being and not just the absence of disease or infirmity.

Incidence—the rate of new cases of disease in a population.

Infectiousness— the relative ease with which an infectious disease is transmitted.

Morbidity—any departure, subjective or objective, from a state of physiological or psychological well-being. Morbidity is generally used to describe non-fatal health events. Sickness.

Mortality—number of deaths or expected deaths in a population; the death rate.

Pandemic—an epidemic occurring over a very wide area, crossing international boundaries and usually affecting large numbers of people. A global disease epidemic.

Population—a group of people defined by some characteristic, such as living in the same place.

Prevalence—the amount of existing disease in a given population at a certain time.

Public health—an effort organized by society to protect, promote, and restore the people’s health. Physicians treat one patient at a time; public health workers treat whole populations.

Risk—the probability that an event will occur (e.g., that an individual will become sick or die) within a stated period of time or at a particular age.

Risk factor—conditions or exposures that can influence the chances that we stay healthy, develop a disease, or die prematurely. Some risk factors are impossible for us to change, like our genes. Other risk factors we can change. The latter are called modifiable risk factors, and include things like our diet, exercise habits, and smoking.

Screening—the use of medical tests or other procedures to identify disease, often at an early stage.

Shift—big changes in the genetics of a virus strain due to mutation. A flu virus may have “shifted” if it is significantly different from strains that have circulated in recent years.

Surveillance—the collection and analysis of timely health information; these data are then used to monitor health and disease in a population.

Transmission—any means of spreading infectious disease to or among people.

(more to be added in the future per request)