Epidemiologists study the patterns, causes and effects of diseases in groups of people and work either in a research setting, focusing on populations as a whole, or as a clinical epidemiologist, concentrating on patients. They focus on the patterns and causes of diseases by using statistics and model-building to find out how they occur. They study samples of the population that include healthy and unhealthy individuals using data given to you. You won't normally collect the data directly from affected groups. The work will inform public health policies and global strategies in order to prevent future outbreaks and epidemics of a disease.