Epidemiology is the study of the distribution of health related events. It is concerned with epidemic of communicable disease, non communicable infectious disease, chronic disease,maternal-child health, occupational health, environment health etc.

1. General Principles of Applied Epidemiology
Summary
The term applied epidemiology is generally used to denote the use or practice of epidemiology to deal with public health issues. As a discipline
of public health, epidemiology instils the spirit of using epidemiological information to promote and protect the health of the public.
Therefore, epidemiology includes science and practice that addresses issues regarding public health.
Epidemiology is: a) a quantitative basic science based on a working knowledge of statistics, probability, and sound research methods; b) a
causal reasoning method based on the development and testing of morbidity and mortality hypotheses; and c) a tool for promoting and
protecting public health action based on science, causal reasoning, and practical common sense.
The term applied epidemiology is generally used to denote the use or practice of epidemiology to deal with public health issues. Applied
epidemiology include:
• Monitoring the reports regarding communicable diseases in the community.
• Studying the influence of a particular dietary component on a person’s risk of developing cancer.
• Evaluating the effectiveness and influence of a cholesterol awareness programme.
• Analysing the historical trends and existing data to plan needs of future public health resources.

3. • The term epidemiology comes from the Greek words epi, meaning “on or upon,” demos, meaning “people,” and
logos, meaning “the study of.” Thus, the following definition of epidemiology captures the basic principles of
epidemiology-
• “Epidemiology is the study of the distribution and determinants of health-related states or events in specified
populations, and the application of this study to the control of health problems.” (MacDonald KL, Spengler RF,
Hatheway CL, et al.)
• This definition of epidemiology reflects some of the fundamental principles of the discipline.
• Study- The study of epidemiology falls in the category of scientific discipline, sometimes refereed as “the basic
science of public health.” It is a sound method of scientific inquiry.
• Distribution- Epidemiology deals with the incidence and pattern of health related events in a population.
• Incidence includes the number of health events as well as the risk or rate of disease in the population.
• Pattern generally refers to the manifestation of health-related issues by place, time, and personal characteristics.
The three characteristics are discussed below-

4. • Time include daily or hourly occurrence, seasonal occurrence, and annual occurrence at the time of an epidemic.
• Place means geographic variation, location of different places like worksites or schools, urban-rural differences, and
such.
• Personal characteristics generally include demographic factors like age, sex, race, marital status, socioeconomic
status, as well as environmental or behavioural exposures.
This principle of distribution is one broad aspect of epidemiology and generally referred to descriptive epidemiology.
Descriptive epidemiology defines the What, Who, When, and Where regarding health-related events.
Determinants- Epidemiology also searches for causes and other factors influencing the occurrence of various health-
related events. Applied epidemiology provide the Why and How of such health events by making group comparisons
with different rates of disease occurrence, variances in demographic features, genetic or immunologic character,
behaviours, environmental exposures, and other potential risk factors. Epidemiologic determinants are very helpful in
providing sufficient evidence to direct immediate and effective public health control and prevention measures.

5. Health-related events- Applied epidemiology is concerned with epidemics of communicable diseases, endemic
communicable diseases, and non-communicable infectious diseases, and even injuries, chronic diseases, birth defects,
maternal-child health, occupational health, and environmental health, behavioural health and well-being.
Specified populations- Epidemiologists are concerned with the collective community health. The epidemiologist
mainly focuses on the exposure (action or source of an illness), number of similarly exposed persons, possibility for
further spread in the community, and preventive interventions for additional cases or recurrences.
Application- As a public health discipline epidemiology provides data for the direction of public health action. An
epidemiologist uses descriptive and analytic scientific methods to diagnose the community health, and also works
upon experience and creativity to plan the method of control and prevention of disease in the community.
Reference:
• MacDonald KL, Spengler RF, Hatheway CL, et al. Type A botulism from sauteed onions.
• JAMA 1985;253:1275-1278.

6. Key Points
Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application
of this study to the control of health problems.” (MacDonald KL, Spengler RF, Hatheway CL, et al.)
Some of the fundamental principles of the discipline are-
Study- The study of epidemiology falls in the category of scientific discipline, sometimes refereed as “the basic science of public health.”
Distribution- Epidemiology deals with the incidence and pattern of health related events in a population.
Incidence includes the number of health events as well as the risk or rate of disease in the population.
Pattern generally refers to the manifestation of health-related issues by place, time, and personal characteristics.
Determinants- Applied epidemiology provide the Why and How of such health events by making group comparisons with different rates of
disease occurrence, variances in demographic features, genetic or immunologic character, behaviours, environmental exposures, and other
potential risk factors.
Health-related events- Applied epidemiology is concerned with epidemics of communicable diseases, endemic communicable diseases, and
non-communicable infectious diseases, and even injuries, chronic diseases, birth defects, maternal-child health, occupational health, and
environmental health, behavioural health and well-being.

7. Specified populations- The epidemiologist mainly focuses on the exposure (action or source of an illness),
number of similarly exposed persons, possibility for further spread in the community, and preventive
interventions for additional cases or recurrences.
Application- An epidemiologist uses descriptive and analytic scientific methods to diagnose the community
health, and also works upon experience and creativity to plan the method of control and prevention of disease
in the community.
Reference:
MacDonald KL, Spengler RF, Hatheway CL, et al. Type A botulism from sauteed onions.
JAMA 1985;253:1275-1278.
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