The sampling method comprises the following steps

Simple random sampling: 1. Lottery method: write down the number of n individuals in the population on the digital label, and put them in a container and mix them evenly. Take one digital label at a time and take it n times continuously, and get a sample with a capacity of n.2. Random number method: sampling the population by looking up a random number table. 2. Systematic sampling: when there are many individuals in the group, the group is divided into balance. 3. Stratified sampling: divide the population into disjoint layers, then independently extract a certain number of individuals from each layer according to a certain proportion, and combine the extracted individuals as samples.

Simple random sampling: survey units are randomly selected from the population without any grouping, classification, queuing, etc.

Repeated sampling: also known as back sampling. The sample units extracted from the population each time are put back into the population after inspection and participate in the next sampling. The characteristic of this sampling is that the probability of each sample unit being extracted in the population is equal.

C. Non-repeated sampling: also known as "non-replacement sampling" and "non-replacement sampling", it is a method of extracting the first sample unit from the whole and the population, and after recording the performance of the relevant signs of the unit, not putting the sample unit back into the whole and the population to participate in the next sampling.

D equidistant sampling: it is to arrange all the units in the population into a graph or list according to a certain sign or order (so-called queuing), and then extract the sample units at equal distance or interval.

E non-probability sampling: also known as unequal probability sampling or non-random sampling, is a method for investigators to sample according to their own convenience or subjective judgment. It does not strictly follow the principle of random sampling.