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• Epidemiology Terms

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• Carrier

A person or animal without apparent disease who harbors a specific infectious agent and is capable of transmitting the agent to others. The carrier state may occur in an individual with an infection that is inapparent throughout its course (known as asymp



• Case

In epidemiology, a countable instance in the population or study group of a particular disease, health disorder, or condition under investigation. Sometimes, an individual with the particular disease.



• Case Definition

A set of standard criteria for deciding whether a person has a particular disease or health-related condition, by specifying clinical criteria and limitations on time, place, and person.



• Case-Control Study

A type of observational analytic study. Enrollment into the study is based on presence (``case'') or absence (``control'') of disease.



• Case-Fatality Rate

The proportion of persons with a particular condition (cases) who die from that condition. The denominator is the number of incident cases; the numerator is the number of cause-specific deaths among those cases.



• Cause Of Disease

A factor (characteristic, behavior, event, etc.) that directly influences the occurrence of disease.



• Cause-Specific Mortality Rate

The mortality rate from a specified cause for a population. The numerator is the number of deaths attributed to a specific cause during a specified time interval; the denominator is the size of the population at the midpoint of the time interval.



• Census

The enumeration of an entire population, usually with details being recorded on residence, age, sex, occupation, ethnic group, marital status, birth history, and relationship to head of household.



• Chain Of Infection

A process that begins when an agent leaves its reservoir or host through a portal of exit, and is conveyed by some mode of transmission, then enters through an appropriate portal of entry to infect a susceptible host.



• Class Interval

A span of values of a continuous variable which are grouped into a single category for a frequency distribution of that variable.



• Cluster

An aggregation of cases of a disease or other health-related condition, particularly cancer and birth defects, which are closely grouped in time and place. The number of cases may or may not exceed the expected number; frequently the expected number is no



• Cohort

A well-defined group of people who have had a common experience or exposure, who are then followed up for the incidence of new diseases or events, as in a cohort or prospective study. A group of people born during a particular period or year is called a b



• Cohort Study

A type of observational analytic study. Enrollment into the study is based on exposure characteristics or membership in a group.



• Common Source Outbreak

An outbreak that results from a group of persons being exposed to a common noxious influence, such as an infectious agent or toxin. If the group is exposed over a relatively brief period of time, so that all cases occur within one incubation period, then



• Confidence Interval

A range of values for a variable of interest, e.g.



• Confidence Limit

The minimum or maximum value of a confidence interval.



• Contact

Exposure to a source of an infection, or a person so exposed.



• Contagious

Capable of being transmitted from one person to another by contact or close proximity.



• Contingency Table

A two-variable table with cross-tabulated data.



• Control

In a case-control study, comparison group of persons without disease.



• Crude Mortality Rate

The mortality rate from all causes of death for a population.



• Cumulative Frequency

In a frequency distribution, the number or proportion of cases or events with a particular value or in a particular class interval, plus the total number or proportion of cases or events with smaller values of the variable.



• Cumulative Frequency Curve

A plot of the cumulative frequency rather than the actual frequency for each class interval of a variable. This type of graph is useful for identifying medians, quartiles, and other percentiles.