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Epidemiology is the study of diseases that affect large numbers of people. This branch of medical science did not become possible until the 1800s, when statistical analysis was applied to the understanding of disease. There are some signs, however, that earlier civilizations were making connections between disease and environmental factors. The ancient Greek physician Hippocrates linked specific diseases to locations, seasons, and climates. In 1865, the French chemist and microbiologist Louis Pasteur showed that a specific organism was causing an epidemic in silkworms. Robert Koch, a German bacteriologist, established the bacterial cause of tuberculosis in humans in 1882.

Toward the mid-1900s, chronic disease epidemiology began, focusing on the rise in peptic ulcer disease, coronary heart disease, and lung cancer. Chronic disease epidemiologists have helped show the links between smoking and lung cancer.

Today, epidemiologists are increasingly interested in global health patterns and in applying new data analytics software and techniques to the field.

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