Epidemiology is the study of the distribution, patterns, and determinants of health and disease in a defined population. It also involves the application of this study to control health problems and improve the health of the populace. Although epidemiology has gained more popularity since the 1950s, its origins are almost 2,500 years old and have been linked to the likes of Hippocrates, John Graunt, William Farr, John Snow, and others.

The core functions of epidemiology include: monitoring the public for diseases (public health surveillance); investigating health events/disease outbreaks; executing analytic studies to identify and quantify the relationship between risk factors and a health outcome; evaluating if health services, facilities, and other related activities would effectively achieve the goal of improving health; linking findings from different fields of science in order to control diseases; and developing health policy based on the evidence gathered. To achieve these tasks, epidemiologists employ the 5Ws: what-the health event or disease of interest; who-the person(s) affected; where-the place the event or disease occurred; when-the time the disease occurred; and why/how-the cause/mode of transmission of the disease.

There are several methods through which the 5Ws are used in epidemiology. These methods are divided into two major categories, i.e., experimental and observational studies. An experimental study is one involving the assignment of participants into different groups in order to determine the causal effect of a certain condition on a certain outcome. Experimental studies are either randomized controlled trials or non-randomized control trials; and are useful in the development of drugs, vaccines, and other medical interventions. On the other hand, an observational study is one in which the effect of a risk factor is observed in a population. Based on which of the 5Ws are answered, observational studies are categorized as descriptive or analytic studies. Descriptive studies answer the who (person), where (place), and when (time) questions; they identify and evaluate health patterns and are used to generate hypotheses about the determinants of disease. Analytic studies answer the why/how (cause/mode of transmission of the disease) question and are concerned with identifying causes and testing the hypotheses generated by the descriptive study.

Given its core functions, as mentioned above, epidemiology is referred to as a cornerstone of public health as it plays a pivotal role in ensuring the existence of a healthy population. Additionally, epidemiology has diversified into various areas of specialization such as cancer epidemiology, cardiovascular epidemiology, clinical epidemiology, environmental and occupational epidemiology, genetic epidemiology, psychiatric epidemiology, pharmaco-epidemiology, nutritional epidemiology, etc., all of which are crucial to the general scope of public health and well-being.

References

1. Centers for Disease, control and Prevention. Lesson 1: Introduction to epidemiology.https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section1.html#:~:text=The%20difference%20is%20that%20epidemiologists,transmission%20(why%2Fhow).
   

2. Bartlett PC, Judge LJ. The role of epidemiology in public health. Rev Sci Tech. 1997 Aug;16(2):331-6. doi: 10.20506/rst.16.2.1020. PMID: 9501345.
   

3. Emory University – Rollins School of Public Health. What is epidemiology. https://www.sph.emory.edu/departments/epi/overview/what-is-epidemiology/index.html.
   

4. Ask Dr. Cath. Descriptive studies. https://www.drcath.net/toolkit/descriptive-studies.
   

5. Stephen B Thacker, Joanna Buffington, Applied epidemiology for the 21st Century, International Journal of Epidemiology, Volume 30, Issue 2, April 2001, Pages 320–325, https://doi.org/10.1093/ije/30.2.32.