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Clinical Care

Prevention, treatment, and management of illness and preservation of mental and physical well‑being through services offered by medical and allied health professions; also known as health care.

Determinant

Factor that contributes to the generation of a trait.

Epidemic

Occurrence in a community or region of cases of an illness, specific health‑related behavior, or other health‑related event clearly in excess of normal expectancy. Both terms are used interchangeably; however, epidemic usually refers to a larger geographic distribution of illness or health‑related events.

Health Outcome

Result of a medical condition that directly affects the length or quality of a person's life.

Intervention

Action or administration that produces an effect or is intended to alter the course of a pathologic process.

Pandemic

Denoting a disease affecting or attacking the population of an extensive region, country, or continent.

Population Health

Approach to health that aims to improve the health of an entire population.

Prevention

Action so as to avoid, forestall, or circumvent a happening, conclusion, or phenomenon (e.g., disease).

Active Immunity

Resistance developed in response to an antigen (i.e., an infecting agent or vaccine), usually characterized by the presence of antibody produced by the host.

Active Surveillance

Public health surveillance in which the health agency solicits reports.

Age-Adjusted Mortality Rate

A mortality rate that has been statistically modified to eliminate the effect of different age distributions among different populations.

Agent

A factor (e.g., a microorganism or chemical substance) or form of energy whose presence, excessive presence, or in the case of deficiency diseases, relative absence is essential for the occurrence of a disease or other adverse health outcome.

Age-Specific Mortality Rate

A mortality rate limited to a particular age group, calculated as the number of deaths among the age group divided by the number of persons in that age group, usually expressed per 100,000.

Alternative Hypothesis

The supposition that an exposure is associated with the health condition under study. The alternative is adopted if the null hypothesis proves implausible.

Analytic Epidemiology

The aspect of epidemiology concerned with why and how a health problem occurs. Analytic epidemiology uses comparison groups to provide baseline or expected values so that associations between exposures and outcomes can be quantified and hypotheses about the cause of the problem can be tested.

Analytic Study

A study, usually observational, in which groups are compared to identify and quantify associations, test hypotheses, and identify causes. Two common types are cohort studies and case-control studies.

Antibody

Any of a variety of proteins in the blood that are produced in response to an antigen as an immune response.

Antigen

Any substance (e.g., a toxin or the surface of a microorganism or transplanted organ) recognized as foreign by the human body and that stimulates the production of antibodies.

Applied Epidemiology

The application or practice of epidemiology to control and prevent health problems.

Arbovirus

Any of a group of viruses that are transmitted between hosts by mosquitoes, ticks, and other arthropods.

Arithmetic Mean

The measure of central location, commonly called the average, calculated by adding all the values in a group of measurements and dividing by the number of values in the group.

Arithmetic-Scale Line Graph

A graph that displays patterns or trends by plotting the frequency (e.g., number, proportion, or rate) of a characteristic or event during some variable, usually time. The y-axis, measuring frequency, uses an arithmetic scale.

Arthropod

An organism that has jointed appendages and segmented external skeleton (e.g., flies, mosquitoes, ticks, or mites).

Association

The statistical relation between two or more events, characteristics, or other variables.

Asymmetrical

A type of distribution where the shape to the right and left of the central location is not the same. Often referred to as a skewed distribution; the mean, median, and mode of an asymmetrical distribution are not the same.

Asymptomatic

Without symptoms.

Attack Rate

A form of incidence that measures the proportion of persons in a population who experience an acute health event during a limited period (e.g., during an outbreak), calculated as the number of new cases of a health problem during an outbreak divided by the size of the population at the beginning of the period, usually expressed as a percentage or per 1,000 or 100,000 population (see also incidence proportion).

Attack Rate, Secondary

A measure of the frequency of new cases of a disease among the contacts of known patients.

Attributable Proportion

A measure of the impact of a causative factor on the public health; the proportion of a health state or event among exposed persons that can be attributed to the exposure also called attributable risk percent.

Attributable Risk Percent

A measure of the impact of a causative factor on the public health; the proportion of a health state or event among exposed persons that can be attributed to the exposure also called attributable risk percent.

Attribute

A risk factor that is an intrinsic characteristic of the individual person, animal, plant, or other type of organism under study (e.g., genetic susceptibility, age, sex, breed, weight).

Axis

One of the dimensions of a graph in a rectangular graph, the x-axis is the horizontal axis, and the y-axis is the vertical axis.

Bar Chart

A visual display in which each category of a variable is represented by a bar or column bar charts are used to illustrate variations in size among categories.

Bar Chart, 100% Component

A stacked bar chart in which all bars or columns are the same length, and the measured axis represents 0%-100%.

Bar Chart, Deviation

A bar chart displaying either positive or negative differences from a baseline.

Bar Chart, Grouped

A bar chart displaying quantities of two variables, represented by adjoining bars or columns (i.e., a group) of categories of one variable, separated by space between groups.

Bar Chart, Stacked

A bar chart displaying quantities of two variables, represented by subdivided bars or columns (the subdivisions representing the categories of one variable) separated by space between bars or columns.

Bias

A systematic deviation of results or inferences from the truth or processes leading to such systematic deviation; any systematic tendency in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth. In epidemiology, does not imply intentional deviation.

Bias, Information

Systematic difference in the collection of data regarding the participants in a study (e.g., about exposures in a case-control study, or about health outcomes in a cohort study) that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.

Bias, Selection

Systematic difference in the enrollment of participants in a study that leads to an incorrect result (e.g., risk ratio or odds ratio) or inference.

Bimodal

Having two data peaks.

Biologic Transmission

Indirect transmission by a vector in which the infectious agent undergoes biologic changes inside the vector as part of its life cycle before it is transmitted to the host.

Birth Cohort

A group of persons born during a particular period or year.

Birth Rate, Crude

The number of live births during a specified period divided by the mid-period population, usually expressed per 1,000 population.

Box Plot

A visual display that summarizes data by using a "box and whiskers" format to indicate the minimum and maximum values (ends of the whiskers), interquartile range (length of the box), and median (line through the box).

Carrier

A person or animal that harbors the infectious agent for a disease and can transmit it to others, but does not demonstrate signs of the disease. A carrier can be asymptomatic (never indicate signs of the disease) or can display signs of the disease only during the incubation period, convalescence, or postconvalescence. The period of being a carrier can be short (a transient carrier) or long (a chronic carrier).

Case

An instance of a particular disease, injury, or other health conditions that meets selected criteria. Using the term to describe the person rather than the health condition is discouraged (see also case-patient).

Case-Control Study

An observational analytic study that enrolls one group of persons with a certain disease, chronic condition, or type of injury (case-patients) and a group of persons without the health problem (control subjects) and compares differences in exposures, behaviors, and other characteristics to identify and quantify associations, test hypotheses, and identify causes.

Case Definition

A set of uniformly applied criteria for determining whether a person should be identified as having a particular disease, injury, or other health condition. In epidemiology, particularly for an outbreak investigation, a case definition specifies clinical criteria and details of time, place, and person.

Case-Fatality Rate

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

Case, Index

The first case or instance of a patient coming to the attention of health authorities.

Case-Patient

In a case-control study, a person who has the disease, injury, or other health condition that meets the case definition (see also case).

Case, Source

The case or instance of a patient responsible for transmitting infection to others; the instance of a patient who gives rise to an outbreak or epidemic.

Cause, Component

A factor that contributes to a sufficient cause.

Cause of Disease

A factor (e.g., characteristic, behavior, or event) that directly influences the occurrence of a disease. Reducing such a factor among a population should reduce occurrence of the disease.

Cause, Necessary

A factor that must be present for a disease or other health problem to occur.

Cause-Specific Mortality Rate

The mortality rate from a specified cause, calculated as the number of deaths attributed to a specific cause during a specified time interval among a population divided by the size of the midinterval population.

Cause, Sufficient

A factor or collection of factors whose presence is always followed by the occurrence of a particular health problem.

Census

The enumeration of an entire population, usually including details on residence, age, sex, occupation, racial/ethnic group, marital status, birth history, and relationship to the head of household.

Central Location

A statistical measurement to quantify the middle or the center of a distribution. Of the multiple ways to define central tendency, the most common are the mean, median, and mode.

Chain of Infection

The progression of an infectious agent that leaves its reservoir or host through a portal of exit, is conveyed by a mode of transmission, and then enters through an appropriate portal of entry to infect a susceptible host.

"Chartjunk"

Unnecessary or confusing visual elements in charts, illustrations, or graphs. The term was first used by Edward Tufte in his book, The Visual Display of Quantitative Information (1983).

Class Interval

The span of values of a continuous variable that are grouped into a single category, usually to create a frequency distribution for that variable.

Class Limits

The values at the upper and lower ends of a class interval.

Clinical Criteria

The medical features (e.g., symptoms, medical examination findings, and laboratory results) that are used in a case definition.

Clinical Disease

A disease that has been manifested by its symptoms and features.

Clinical Trial

An experimental study that uses data from individual persons. The investigator specifies the type of exposure for each study participant and then follows each person's health status to determine the effects of the exposure.

Cluster

An aggregation of cases of a disease, injury, or other health condition (particularly cancer and birth defects) in a circumscribed area during a particular period without regard to whether the number of cases is more than expected (often the expected number is not known).

Cohort

A well-defined group of persons who have had a common experience or exposure and are then followed up, as in a cohort study or prospective study, to determine the incidence of new diseases or health events.

Cohort, Birth

A group of persons born during a particular period or year.

Cohort Study

An observational analytic study in which enrollment is based on status of exposure to a certain factor or membership in a certain group. Populations are followed, and disease, death, or other health-related outcomes are documented and compared. Cohort studies can be either prospective or retrospective.

Common-Source Outbreak

An outbreak that results from persons being exposed to the same harmful influence (e.g., an infectious agent or toxin). The exposure period can be brief or can extend over days, weeks, or longer, with the exposure being either intermittent or continuous.

Community Immunity

The resistance to an infectious agent of an entire group or community (and, in particular, protection of susceptible persons) as a result of a substantial proportion of the population being immune to the agent. Herd immunity is based on having a substantial number of immune persons, thereby reducing the likelihood that an infected person will come in contact with a susceptible one among human populations, also called community immunity.

Community Trial

An experimental study that uses data from communities. The investigator specifies the type of exposure for each community and then follows the communities' health status to determine the effects of the exposure.

Comparison Group

A group in an analytic study (e.g., a cohort or case-control study) with whom the primary group of interest (exposed group in a cohort study or case-patients in a case-control study) is compared. The comparison group provides an estimate of the background or expected incidence of disease (in a cohort study) or exposure (in a case-control study).

Confidence Interval

A range of values for a measure (e.g., rate or odds ratio) constructed so that the range has a specified probability (often, but not necessarily, 95%) of including the true value of the measure.

Confidence Limits

The end points (i.e., the minimum and maximum values) of a confidence interval.

Confounding

The distortion of the association between an exposure and a health outcome by a third variable that is related to both.

Contact

Exposure to a source of an infection / A person who has been exposed.

Contact, Direct

Exposure or transmission of an agent from a source to a susceptible host through touching (e.g., from a human host by kissing, sexual intercourse, or skin-to-skin contact) or from touching an infected animal or contaminated soil or vegetation.

Contagious

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

Contingency Table

A two-variable table of cross-tabulated data.

Continuous Variable

A variable that has the potential for having an infinite number of values along a continuum (e.g., height and weight).

Control

In a case-control study, a member of the group of persons without the health problem under study.

Crude

When referring to a rate, an overall or summary rate for a population, without adjustment.

Crude Birth Rate

The number of live births during a specified period divided by the mid-period population, usually expressed per 1,000 population.

Crude Death Rate

A mortality rate from all causes of death for an entire population, without adjustment.

Crude Mortality Rate

A mortality rate from all causes of death for an entire population, without adjustment.

Cumulative Frequency

In a frequency distribution, the number or proportion of observations with a particular value and any smaller value.

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 and quartiles and other percentiles.

Death-to-Case Ratio

The number of deaths attributed to a particular disease, injury, or other health condition during a specified period, divided by the number of new cases of that disease, injury, or condition identified during the same period.

Decision Analysis

Application of quantitative methods to decision-making.

Decision Tree

A branching chart that represents the logical sequence or pathway of a clinical or public health decision.

Demographic Information

Personal characteristics of a person or group (e.g., age, sex, race/ethnicity, residence, and occupation) demographic information is used in descriptive epidemiology to characterize patients or populations.

Dendrogram

See phylogenetic tree.

Denominator

The lower portion of a fraction; used in calculating a ratio, proportion, or rate. For a rate, the denominator is usually the midinterval population.

Dependent Variable

In a statistical analysis, a variable whose values are a function of one or more other variables.

Descriptive Epidemiology

The aspect of epidemiology concerned with organizing and summarizing data regarding the persons affected (e.g., the characteristics of those who became ill), time (e.g., when they become ill), and place (e.g., where they might have been exposed to the cause of illness).

Determinant

Any factor that brings about change in a health condition or in other defined characteristics.

Direct Transmission

Immediate transfer of an agent from a reservoir to a host by direct contact or droplet spread.