Principles of Epidemiology | Lesson 1 (2023)

Section 1: Definition of Epidemiology

Students of journalism are taught that a good news story, whether it be about a bank robbery, dramatic rescue, or presidential candidate’s speech, must include the 5 W’s: what, who, where, when and why (sometimes cited as why/how). The 5 W’s are the essential components of a news story because if any of the five are missing, the story is incomplete.

The same is true in characterizing epidemiologic events, whether it be an outbreak of norovirus among cruise ship passengers or the use of mammograms to detect early breast cancer. The difference is that epidemiologists tend to use synonyms for the 5 W’s: diagnosis or health event (what), person (who), place (where), time (when), and causes, risk factors, and modes of transmission (why/how).

The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. In other words, the word epidemiology has its roots in the study of what befalls a population. Many definitions have been proposed, but the following definition captures the underlying principles and public health spirit of epidemiology:

(Video) Principles Of Epidemiology Part 1

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 (1).

Key terms in this definition reflect some of the important principles of epidemiology.


Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among persons with disease, differs from what might be expected. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences.

In fact, epidemiology is often described as the basic science of public health, and for good reason. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.(2)


Epidemiology is concerned with the frequency and pattern of health events in a population:

Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population. The resulting rate allows epidemiologists to compare disease occurrence across different populations.

Pattern refers to the occurrence of health-related events by time, place, and person. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures.

(Video) Principles of Epidemiology

Characterizing health events by time, place, and person are activities of descriptive epidemiology, discussed in more detail later in this lesson.


Determinant: any factor, whether event, characteristic, or other definable entity, that brings about a change in a health condition or other defined characteristic.

Epidemiology is also used to search for determinants, which are the causes and other factors that influence the occurrence of disease and other health-related events. Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. They assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, or other so-called potential risk factors. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures.

Health-related states or events

Epidemiology was originally focused exclusively on epidemics of communicable diseases (3) but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health. Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied.

Specified populations

Although epidemiologists and direct health-care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.” The clinician is concerned about the health of an individual; the epidemiologist is concerned about the collective health of the people in a community or population. In other words, the clinician’s “patient” is the individual; the epidemiologist’s “patient” is the community. Therefore, the clinician and the epidemiologist have different responsibilities when faced with a person with illness. For example, when a patient with diarrheal disease presents, both are interested in establishing the correct diagnosis. However, while the clinician usually focuses on treating and caring for the individual, the epidemiologist focuses on identifying the exposure or source that caused the illness; the number of other persons who may have been similarly exposed; the potential for further spread in the community; and interventions to prevent additional cases or recurrences.

(Video) Introduction to Epidemiology: History, Terminology & Studies | Lecturio


Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. Like the practice of medicine, the practice of epidemiology is both a science and an art. To make the proper diagnosis and prescribe appropriate treatment for a patient, the clinician combines medical (scientific) knowledge with experience, clinical judgment, and understanding of the patient. Similarly, the epidemiologist uses the scientific methods of descriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community.


Epidemiology is the study (scientific, systematic, data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (patient is community, individuals viewed collectively), and the application of (since epidemiology is a discipline within public health) this study to the control of health problems.

Principles of Epidemiology | Lesson 1 (1) Exercise 1.1

Below are three key terms taken from the definition of epidemiology, followed by a list of activities that an epidemiologist might perform. Match the term to the activity that best describes it. You should match only one term per activity.

  1. Distribution
  2. Determinants
  3. Application
  1. ____ 1. Compare food histories between persons with Staphylococcus food poisoning and those without
  2. ____ 2. Compare frequency of brain cancer among anatomists with frequency in general population
  3. ____ 3. Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site
  4. ____ 4. Graph the number of cases of congenital syphilis by year for the country
  5. ____ 5. Recommend that close contacts of a child recently reported with meningococcal meningitis receive Rifampin
  6. ____ 6. Tabulate the frequency of clinical signs, symptoms, and laboratory findings among children with chickenpox in Cincinnati, Ohio

Check your answer.

References (This Section)

  1. Last JM, editor. Dictionary of epidemiology. 4th ed. New York: Oxford University Press; 2001. p. 61.
  2. Cates W. Epidemiology: Applying principles to clinical practice. Contemp Ob/Gyn 1982;20:147–61.
  3. Greenwood M.Epidemics and crowd-diseases: an introduction to the study of epidemiology, Oxford University Press; 1935.

Next Page: Historical Evolution of Epidemiology

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Lesson 1 Overview

(Video) PubH 6003: Principles and Practice of Epidemiology | MPH@GW

(Video) Principles of Epidemiology Part 1


What are the principles of epidemiology lesson 1 section 8? ›

Section 8: Concepts of Disease Occurrence. A critical premise of epidemiology is that disease and other health events do not occur randomly in a population, but are more likely to occur in some members of the population than others because of risk factors that may not be distributed randomly in the population.

What are the 5 principles of epidemiology? ›

In the mid-1980s, five major tasks of epidemiology in public health practice were identified: public health surveillance, field investigation, analytic studies, evaluation, and linkages.

What questions does epidemiology answer? ›

Epidemiologist want to know what causes disease; how does disease spread; what can prevent disease and/or keep a population mentally, socially, and physically healthy; and what can be done to control disease. Distribution: Frequency and pattern of health outcomes or exposures in a population.

What are the key principles of epidemiology? ›

The difference is that epidemiologists tend to use synonyms for the 5 W's: diagnosis or health event (what), person (who), place (where), time (when), and causes, risk factors, and modes of transmission (why/how).

What is phc6001 principles of epidemiology in public health? ›

PHC 6001: Principles of Epidemiology in Public Health

Includes distribution and determinants of health-related states or events in specific populations and application to control of health problems.

What is epidemiology as defined in this lesson? ›

Epidemiology is: a) a quantitative basic science built on a working knowledge of probability, statistics, and sound research methods; b) a method of causal reasoning based on developing and testing hypotheses pertaining to occurrence and prevention of morbidity and mortality; and c) a tool for public health action to ...

Is epidemiology a lot of math? ›

Epidemiology combines science and mathematics to study the distribution of disease within a population and the factors that influence disease. At its core, epidemiology uses basic math skills to determine the distribution and cause of diseases.

Is epidemiology a hard class? ›

These are generally offered as separate courses. Yes, they can be difficult, particularly if you have been away from studying for a time — as in practicing clinicians. If you are still in your undergraduate studies, I would recommend taking a statistics class while you are still in university.

How do I prepare for epidemiology? ›

Recommended fields of study at the undergraduate level include biostatistics, health science or nursing. Students also pursue degrees in biology, chemistry or public health. While a specific field of study isn't required, coursework typically includes statistics, social sciences, biology and chemistry.

What are the 3 key terms used in epidemiology? ›

EPIDEMIOLOGIC TRIAD. The traditional model of infectious disease causation. Includes three components: an external agent, a susceptible host, and an environment that brings the host and agent together, so that disease occurs.

What are the 4 important elements of epidemiology? ›

Epidemiology utilizes an organized approach to problem solving by: (1) confirming the existence of an epidemic and verifying the diagnosis; (2) developing a case definition and collating data on cases; (3) analyzing data by time, place, and person; (4) developing a hypothesis; (5) conducting further studies if ...

What are the 3 types of epidemiology? ›

Three major types of epidemiologic studies are cohort, case-control, and cross-sectional studies (study designs are discussed in more detail in IOM, 2000).

What are the 4 stages of epidemiology? ›

The four epidemiological stages of IBD are Emergence, Acceleration in Incidence, Compounding Prevalence and Prevalence Equilibrium.

What are the 7 steps in the epidemiology investigation? ›

Section 2: Steps of an Outbreak Investigation
  • Prepare for field work.
  • Establish the existence of an outbreak.
  • Verify the diagnosis.
  • Construct a working case definition.
  • Find cases systematically and record information.
  • Perform descriptive epidemiology.
  • Develop hypotheses.
  • Evaluate hypotheses epidemiologically.

What are the key 6 characteristics of epidemiology? ›

It extracts six types of epidemiological characteristic: design of the study, population that has been studied, exposure, outcome, covariates and effect size.

Why do we need principles of epidemiology? ›

Epidemiology provides data for directing public health action. The information is used when planning how to control and prevent disease in the community. Through public health surveillance, a health systematically collects, analyzes, interprets and disseminates health data on an ongoing basis.

What is ethical principles in epidemiology? ›

The ethical issues that arise in. epidemiology can be summed up in. the concepts of autonomy, non- maleficence, beneficence and justice. Autonomy is the term we use to.

What is epidemiology in simple words? ›

By definition, epidemiology is the study (scientific, systematic, and data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (neighborhood, school, city, state, country, global).

What is epidemiology explained to dummies? ›

Epidemiology is the study of distribution and determinants of injury and disability. It describes the health status of populations, explains the causes of disease and is used to predict the occurrence of disease in the future.

What is epidemiology and examples? ›

The term epidemiology is now widely applied to cover the description and causation of not only epidemic, infectious disease, but of disease in general, including related conditions. Some examples of topics examined through epidemiology include as high blood pressure, mental illness and obesity.

Is epidemiology good for med school? ›

Knowledge of epidemiology is also valuable for any student or physician who wants to become involved in clinical or population health research. In fact, one student who worked with us last year was recruited to join a clinical research team as an undergraduate student because she had taken a course in epidemiology.

Do you need to know calculus for epidemiology? ›

Before enrolling in required statistics classes for your PhD or MS in Epidemiology, you must have taken at least 2 quarters or 2 semesters of differential and integral calculus, and a course in introductory statistics.

What kind of math is used in epidemiology? ›

Dynamical systems and differential equations, graph theory, and probability theory/stochastic processes, are at the heart of epidemiology.

Why is epidemiology so hard? ›

This requires designing a study that is correct, feasible, applicable, and robust enough to draw conclusions. One of the challenges of epidemiological research is that it can be difficult to design studies that are able to accurately measure the factors that are associated with a given health outcome.

What should I study for epidemiology? ›

To enter graduate programs in epidemiology, applicants typically need a bachelor's degree in a field such as biology, public policy and social services, or social science. Epidemiology programs include coursework in public health, biological and physical sciences, and math and statistics.

Does epidemiology count as science GPA? ›

Osteopathic (DO) medical programs compute a “Science GPA” that does not include Math but does include Biological Anthropology, Engineering, Epidemiology, and Public Health (see AACOMAS Course Subjects Guide ). Veterinary medical programs have a similar system to DO (see VMCAS Course Subjects Guide ).

Do epidemiologists need to be good at math? ›

A prospective epidemiologist needs a strong foundation in math and science, particularly life sciences and statistics. Epidemiologists often work with computer models, so computer skills are important.

How long does it take to study epidemiology? ›

It may also depend on the education required — while most epidemiologist jobs require a master's degree, some may require doctoral degrees as well. When you consider school, certification and work experience, it may take up to six years or longer to become an epidemiologist.

Is there chemistry in epidemiology? ›

There is an interdisciplinary interface between analytical chemistry and epidemiology studies with respect to the design, execution, and analysis of environmental epidemiology cohorts and studies.

What are the two parts of epidemiology? ›

Often, however, epidemiology provides sufficient evidence to take appropriate control and prevention measures. Epidemiologic studies fall into two categories: experimental and observational.

What is the most basic measure in epidemiology? ›

Simplest & most basic measure – absolute number of persons who have disease or characteristic of interest.

What are the 2 major categories for epidemiological studies? ›

Epidemiologists conduct two main types of analytic studies: experimental and observational.

What are the types of questions in epidemiology? ›


For the same exposure outcome pair, epidemiologists tend to ask 3 main types of questions: descriptive, predictive, and causal (5).

What does epidemiology investigate? ›

The purpose of the epidemiologic investigation is to identify a problem, collect data, formulate and test hypotheses. It involves the collection and analysis of more facts or data to determine the cause of illness and to implement control measures to prevent additional illness.

What are the 5 specific objectives of epidemiology? ›

Objectives of Epidemiology
  • identify the etiology or cause of disease.
  • determine the extent of disease.
  • study the progression of the disease.
  • evaluate preventive and therapeutic measures for a disease or condition.
  • develop public health policy.


1. Epidemiological Studies: A Beginners guide
(Let's Learn Public Health)
2. Principles of Epidemiology: Sources of Public Health Data
(Charles Edeki -- Math Computer Science Programming)
3. Introduction to Principles of Epidemiology
(Razif Shahril)
4. Epidemiology Introduction | Epidemiology Definition | Important Principles of Epidemiology
5. Introduction to Community Medicine. (part 1) Principles of epidemiology.
(Medical lectures )


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