It has been said that “Some observers of epidemiology appear to believe that epidemiology is little more than the application of statistical methods to the problems of disease occurrence and causation. In reality, epidemiology is much more than finely dressed statistics. It is a scientific discipline with roots in biology, logic and the philosophy of science. For epidemiologists, statistical methods serve as an important tool, but not as a foundation. For some, epidemiology is too simple to warrant serious attention, and for others it is too convoluted to understand.” quotation taken from: An Introduction to Epidemiology by Kenneth J. Rothman, Oxford University Press, 2002.
Epidemiology is the study of disease in populations and the factors that contribute to the development of disease. The population under study may be an entire population of cats living in a cattery, a sample of a population of cats living in a city, a sample of horses stabled in a training yard or it may even be a single breed of dog.
Epidemiology is an ancient field, dating back to the time of Hippocrates around 400 BC. Epidemiology is a continuum with the focus on groups of subjects rather than individuals. The spectrum of epidemiological activities stretches from demography (census taking) through survey research and observational studies to experimental medicine (clinical trials).
It can be said that epidemiologists watch the world as it is in order to make observations (often with no hope of controlling anything), and accept that the interplay of many factors may influence the phenomenon they are trying to study. They then rely on the theory of biology and the application of statistical methods to control for the effects of measured external factors.
Epidemiologists study a wide range of health conditions as well as the impact that various exposures have on the development of disease. Epidemiologists carry out studies to describe and evaluate the occurrence of disease at the population level rather than in the individual patient or pet. Epidemiologists are also involved in the application of the knowledge gained to the control of health problems in populations. By understanding the patterns of disease occurrence, epidemiology encourages the development of the most appropriate means of prevention and control. Clinical trials are a specific type of epidemiological study that are designed to evaluate how well different treatments work.
Surveillance is the ongoing, and often continuous, collection, analysis, interpretation and communication of health information. Surveillance allows us to follow, in both time and space, the health status and risk factors associated with disease in a given population.
Epidemiology is an essential tool for the study of the ecology and description of the natural history of disease, health surveillance, disease detection and disease outbreak investigation. What has been described as "shoe-leather" epidemiology refers to the door-to-door interviews that have been used to identify affected individuals (cases) and unaffected individuals (controls) in an outbreak or disease investigation. This type of epidemiological technique is invaluable in identifying risk factors and potential causes of disease.
The field of clinical epidemiology is said to be ‘clinical’ as it seeks to answer clinical questions and to guide clinical decision making and ‘epidemiology’ as it focuses on the care of individual patients in the context of the larger population and the methods used to answer clinical questions. At the clinical level, the principles of epidemiology provide tools for evaluating methods of diagnosis and treatment in the clinical environment. The principles of epidemiology are essential in clinical medicine because there are wide variations in the expression of disease between individuals. If all individuals responded identically to a disease or its treatment, then we would be able to do detailed experiments on one animal and know how to diagnose, treat and prevent that condition in all others of that breed.
