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epidemiology. the science concerned with the study of the factors determining and influencing the frequency and distribution of disease, injury, and other health-related events and their causes in a defined human population for the purpose of establishing programs to prevent and control their development and spread.
Both incidence and prevalence are words used in the field of epidemiology. Epidemiology is a branch of medicine that looks at (you probably guessed it) how many people have a particular disease, what the risks are of contracting a disease, what happens to people who get that disease, and ultimately, how to prevent disease from occurring.