1. 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

2. • 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.

3. • 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.

4. • 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.

5. • 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.

6. • 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.

7. • 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

8. • 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.

9. • 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.

10. • 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.

11. • 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.

12. • 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.

13. • 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.

14. • 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.

15. • 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.

16. • 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.

17. • 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.

18. • 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.

19. • 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.

20. • 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, a
nnulments, separations, and health events that
are based on registration of these events.