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Epidemiology is the study of what the effects of health and disease conditions are in certain populations. These doctors perform evidence-based studies that are important in setting up protocols regarding public health.

Epidemiologists perform various evidence-based studies that look at analyzing causes, patterns and the effect of certain conditions and disorders in populations around the world. Epidemiology is very important for public health as the evidence-based research done by these doctors helps to identify risk factors for certain diseases, and helps setup goals for preventative healthcare. These studies will then result in appropriate protocols and policies being setup in public healthcare.

This discipline has helped to develop methodologies that are currently being used in clinical research and public health studies. The duties of an epidemiologist includes helping with the study designs, the collection, statistical analysis and interpretation of data and disseminating the results. The major areas where epidemiologists focus on include the cause or aetiology of a disease, disease surveillance, outbreak investigation, screening, disease transmission, biomonitoring and comparing the effects of treatments in clinical trials.

Clinical trials used in Epidemiology

Case series

These trials are qualitative studies looking at the clinical findings of a single patient or a small group of patients who are diagnosed with the same illness or condition. This would be a descriptive study and can't be used to interpret findings to relate to the general population.

Case series studies can also be used as a statistical technique that compares periods during which patients are exposed to a factor that has the potential to cause an illness, with periods when they are not exposed to that factor. In this instance, the study is described as self-controlled where individual patient follow-up time is divided into exposed and unexposed periods. An example of where results from such studies are used is in that of adverse events to vaccinations. 

Case-control studies

These are retrospective studies where a group of patients, that have a certain disease, is compared with a group of individuals who don't have the disease. The latter is called the "control group" and they should come from the same population as the patients who do have the disease. The case-control study then looks back in time at any potential exposures that both groups may have encountered and the results are compared between them.

Cohort studies

This study looks at subjects who are at risk of contracting an illness or being diagnosed with the condition that is under investigation. This would then mean that the test subject should be free of the disease when the cohort study starts. The study subjects are then followed up to assess what their outcomes are regarding the condition that is being investigated. An example of a cohort study would be investigating the long-term cardiovascular outcomes of obese versus non-obese patients.

A cohort study is different to a case-control study, as the former compares a disease outcome between two population groups versus the latter where two groups of individual are being retrospectively compared relative to a condition existing in one group and not the other.

Outbreak investigation

An epidemiologist will identify the existence of an outbreak and then try and verify if a certain diagnosis is related to the outbreak. A hypothesis will be developed to determine the cause of the problem and then data will be collected so that the analysis of the situation can be performed. 

If the study yields information regarding a connection between a disease and an outbreak in the environment, control and prevention systems will then be developed and implemented.

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