What is Epidemiology and why is it important?

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:
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). To continue reading about the definition of epidemiology visit the book developed by the Centers for Disease Control and Prevention (CDC) available here.

The CDC breaks this definition down into the important principles of epidemiology, check it here
The most common types of epidemiological studies are case studies, cross sectional studies and cohort studies:

  • Case studies describe characteristics of a group of people who have the same disease or the same exposure. Its major aim is to understand the demographics, presentation and prognostics.
  • Cross sectional studies take a selected population, that is representative of the whole population and measure health information at a certain point in time. They are also known as prevalence studies when they measure the number of people with a disease at a particular point in time.
  • Cohort studies follow a group of people during a certain period of time in order to collect information about the risk factors. Its main purpose is to compare outcomes between the people who were exposed to a certain risk factor (example: disease), and those who were not.

For further information:

  • Let's Learn Public Health prepared a video, where an overview of the most common types of epidemiological studies, their advantages and disadvantages is given.  It also looks at systematic reviews and meta-analysis. Watch it below:




  1. Introduction to Epidemiology. Lesson 1 in: Centers for Disease Control and Prevention. Principles of Epidemiology in Public Health Practice, An Introduction to Applied Epidemiology and Biostatistics. https://www.cdc.gov/OPHSS/CSELS/DSEPD/SS1978/Lesson1/Section1.html (accessed April 2021)

Prevalence and Incidence: two relevant concepts

An array of measures is employed in epidemiology. Two important epidemiologic measures are prevalence and incidence – Prevalence refers to the ratio between the number of patients with a particular disease in a population and the number of people in that population. Incidence refers to the number of individuals who develop a specific disease during a particular time period. The key difference between these two epidemiologic measures is that incidence only considers new cases, prevalence includes new and pre-existing cases. 

For better understanding, following videos are available:

  • The Medmastery has developed a video named “Incidence and Prevalence - Everything you need to know” that is ideal for anyone who’s just diving into clinical epidemiology. Watch it below
  •  The Relationship Between Incidence and Prevalence

If you wish to know more about the epidemiology of CDG, the CDG&Allies-PPAIN team made a toolkit available for the community, consisting of a literature review regarding the published epidemiological data on CDG (which is expected to be published in 2022); an infographic, a powerpoint presentation and the recording of the session about epidemiology during the 5th World CDG Conference! If you wish to access the later three, you need to be registered in our platform (log in /create new account HERE). For further information, don’t hesitate to contact us! You just have to fill the contact form and explain how we can help you! 

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Ana Piedade, Sci and Volunteer Program 2021, NOVA School of Science and Technology, Portugal.


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Page modified at Friday, May 20, 2022 - 15:48