(1) high-risk population or (and) susceptible population;
⑵ Sampling survey: According to the principle of randomness, some research units are randomly selected from the research population as the survey objects.
2. Content; It mainly includes the measurement of biochemical and physiological functions of disease rate by measuring instruments.
⑴ The measurement indicators of disease frequency include: morbidity, morbidity and mortality, or the specific incidence of various diseases.
⑵ Determination of biochemical and physiological functions: including indicators and methods of physiology, biochemistry, hematology, immunology, imaging, genetics and molecular biology.
3. Evaluation of the relationship between exposure and health effects: The measurement results of exposure and health effects should be analyzed by correct epidemiological methods and health statistics methods. Make a correct evaluation according to the analysis data and scientific principles. Among them, mixed factors and causal judgment are particularly noteworthy.