Definition of Terms Epidemiology

Dr. Bhoj R singh, Principal Scientist (VM)I/C Epidemiology; Centre for Animal Disease Research and Diagnosis

Indian Veterinary Research Institute, Izatnagar-243122, Bareilly, UP, India. TeleFax  +91-581-2302188

• Agent A causative factor, such as a biological or

chemical agent that must be present (or absent) in the environment for disease occurrence in a suspectible host.

• Analytic epidemiologic studies Study designs that examine groups of individuals

in order to make comparisons and associations and to determine causal relationships; also known as cohort, cross-sectional, and case-control studies.

• Attack rate

The number of cases of disease in a specific population divided by the total population at risk for a limited time period, usually expressed as a percentage.

• Attributable risk percentage A statistical measure that estimates the number of cases of a disease attributable to the exposure of interest.

• Bias

An error in the study design caused by the tendency of researchers to expect certain conclusions on the basis of their own personal beliefs that results in incorrect conclusions regarding the association between potential risk factors and disease occurrence.

• Case fatality rate

Refers to deaths from a specific disease.• Case reports

Client (case) history studies used in epidemiologic descriptive studies.

• Case series A compilation of case reports.• Case-control study An analytic epidemiologic study design

that assembles study groups after a disease has occurred; also called a retrospective study.

• Cause-specific death rate Number of deaths from a specific cause;

expressed as a number per 100,000 population.

• Chemical agents Includes poisons and allergens.• Cohort study An analytic epidemiologic study design that

assembles study groups before disease occurrence to observe and compare the rates of a health outcome over time; also called a prospective study.

• Co-relational study A descriptive epidemiologic study design used

to compare aggregate populations for potential exposures of disease.

• Cross- sectional survey A descriptive epidemiologic study design that

uses a representative sample of the population to collect information on current health status, personal characteristics, and potential risk factors or exposures at one point in time.

• Demography The statistical science or study of populations,

related to age-specific categories, birth and death rates, marital status, and ethnicity.

• Descriptive epidemiologic studies Epidemiologic study designs that contribute to

the description of a disease or condition by examining the essential features of person, place, and time.

• Disease frequency

Occurrence of disease as measured by various rates such as morbidity rate.

• Ecology

The study of relations and interactions among all organisms within the total environment; in community health, the individual’s interaction with his or her social, cultural, and physical environments.

• Environment Internal and external factors that constitute the context

for agent-host interactions; the aspect of existence perceived outside the self; this perception changes with alterations in awareness and expansion of consciousness; one of the concepts of nursing metaparadigm.

• Epidemic A number of cases of an infectious agent or disease

(outbreak) clearly in excess of the normally expected frequency of that disease in that population.

• Eidemiology An applied science that studies the distribution and

determinants of health-related states or events in populations.

• False-negative test A screening test result that is negative

when the individual actually has the disease of interest.

• False-positive test A screening test result that is positive

when the individual does not have the disease of interest.

• Host A person or living species capable of

being infected.

• Incidence rate

The rate of new cases of a condition or disease in a population in a specified time period; provides an estimate of the condition/disease risk in that population.

• Infectious agents

Bacteria, fungi, viruses, metazoa, and protozoa.

• Intervention study

Epidemiologic study design that is experimental in nature and used to test a hypothesis about a cause-and-effect relationship.

• Levels of prevention A three-level model of intervention (primary,

secondary, tertiary) used in the epidemiologic approach, designed to prevent or to halt or reverse the process of pathological change as early as possible in order to prevent damage.

• Maternal mortality rate Deaths of mothers at time of birth, expressed as

a number per 100,000 live births.• Measures of association Statistical analysis methods used to investigate

the relationship between two or more variables or events.

• Morbidity rate A disease rate, specifically prevalence and

incidence rates of diseases in a population in a specified time period.

• Mortality rate The number of deaths from all causes divided by

the total population at a particular time and place.

• Natural history of a disease The course that a disease would take from onset

to resolution without intervention by humans.

• Nutritive elements

Substances such as vitamins or proteins that, if excessive or deficient, act as an agent of disease.

• Observational studies

Non-experimental studies that describe, compare, and explain disease occurrence.

• Odds ratio A statistical measure of association reflecting the

ratio of two odds reflecting the relative risk (RR) when the specific risk of disease of both the exposed and the unexposed groups is low. Calculated when incidence rates are unavailable.

• Physical agents Agents of disease that must be present or

absent for a problem to occur. Examples include radiation, excessive sun exposure, and mechanical agents.

• Point prevalence

The total number of persons with a disease at a specific point of time.

• PRECEDE-PROCEED model

A health–promotion planning framework useful in applying the epidemiologic approach to community health planning.

• Prevalence rate

A proportion or percentage of a disease or condition in a population at any given time.

• Prevention trials

An epidemiologic intervention study design used to compare measures or interventions aimed at the prevention of disease.

• Prospective study

An epidemiologic study design that assembles study groups before disease occurrence.

• Relative risk

An epidemiologic measure of association that indicates the likelihood that an exposed group will develop a disease or condition relative to those not exposed.

• Retrospective study

An epidemiologic study design that assembles study groups after disease occurrence.

• Risk

The probability that an event, outcome, disease, or condition will develop in a specified time period.

• Sensitivity The probability that an individual who has the disease of

interest will have a positive screening test result.• Specificity The probability that an individual who does not have the

disease of interest will have a negative screening test result.

• Surveillance The systematic collection and evaluation of all aspects of

disease occurrence and spread, resulting in information that may be useful in the control of the disease.

• Therapeutic trials

An epidemiologic intervention study design used to compare measures or interventions aimed at therapeutic benefits.

• Vital statistics

Systematically tabulated data on vital events such as births, deaths, marriages, divorces, adoptions, annulments, separations, and health events that are based on registration of these events.