Trial investigation generally belongs to the investigation conducted in a simulated real environment. The trial investigation is experimental, but not formal. Formal investigation refers to the investigation according to the relevant regulations and requirements, that is, according to the actual situation and various rules and regulations. A formal investigation of the incident is often made public.
Survey type
1. Simple random sampling: Also known as pure random sampling, it refers to the sampling unit directly extracted from the crowd for observation without any treatment, classification or exclusion. Theoretically, it is the most consistent with the principle of randomness of sampling survey, and it is also the most basic form of sampling survey. Specific methods are: direct selection, lottery, random number table.
2. Stratified sampling: also known as type sampling or classified sampling. Firstly, the overall unit is stratified according to the main signs, and then several sample units are randomly selected from each layer, and the sample units of each layer form a sample.