Epidemiology is the study of how and why diseases occur in different groups of people (populations). It looks for patterns and trends in illness to work out why certain diseases, such as cancer, occur in some people but not in others. For example, it compares the health of people who have different lifestyles or occupations, live in different regions or come from different countries, and tries to determine the impact on health.
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The key areas of epidemiology
The key areas of epidemiology include:
Health services research – This investigates the quality of, and ease of access to, health services such as hospitals, specialists and allied health care practitioners. The aim is to find the best ways to help patients at all stages of disease and improve safety. Health services research also works out how much health care costs and can help identify where to direct funds for staffing, medical equipment and therapies.
Research into cancer causes – Researchers examine medical data, often from many hundreds or thousands of people, to understand what causes cancer and how it might be prevented. Research into the causes of cancer focuses on groups of people rather than individuals.
Modelling – This is a mathematical way of using information from the past to estimate what might happen in the future. For example, researchers use modelling to work out how many people are likely to be diagnosed with cancer in 10 years time, or how much funding will be needed to run a cancer screening program.
Types of population studies
The two most common types of population studies used in epidemiology include:
Cohort studies – These set out to answer the question, ‘What will happen to me?’ This involves identifying a large number of people, collecting information about them at the beginning of the study, either from medical records or through surveys, and then watching them over a period of time to see what happens to their health. Cohort studies are also called prospective studies.
Case control studies – These aim to answer the question, ‘why me?’ A case control study compares people who have a disease (the cases) with people who don’t have the disease but are otherwise similar (the controls). The study then looks back over a period of time to see if exposure to something in particular (e.g. at work, in the environment, lifestyle) was more likely in the group with the condition than in the group without. In some cases, the researchers may look at medical records. Case control studies are also called retrospective studies because they look back.