Commonly used survey methods are:
① Cross-sectional investigation: investigate what is happening or existing at the site.
② Prospective investigation: This is a method of designing exposed and unexposed groups in advance, observing their reactions, and finally analyzing the "cause and effect" of the results of the two groups.
⑨ Retrospective investigation: This is a method to compare the morbidity or mortality of exposed group and unexposed group through retrospective investigation after the phenomenon occurs. This is a kind of "from effect to cause"
Method.
(4) Follow-up survey: This is a survey method for long-term uninterrupted follow-up observation of the observed objects.