1. Epidemiology is a science that studies the distribution of diseases and health status in the population and its influencing factors, explores the causes of diseases, and studies strategies and measures to prevent and treat diseases and promote health.
2. Quasi-experiment (semi-experiment and quasi-experiment): A complete field study should have four basic characteristics of experimental research, namely, setting control, random distribution, human intervention and prospective tracking. If an experimental study lacks one or several characteristics, it becomes an experimental study.
3. Incidence rate: the frequency of new cases of diseases in a certain period of time for a specific population. The formula is: the number of new cases of a certain disease in a certain period/the number of exposed people in the same period × K.