The method of extracting sample units from the whole and the whole is as follows

1. Draw lots: write down the number of n individuals in the population on the digital label, and put them into a container and mix them evenly. Draw one digital label at a time and draw it n times in a row, and get a sample with a capacity of n.2. Random number method: sampling the population by looking up a random number table.

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

Repeated sampling: also called put-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.

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 whole, and after recording the performance of the relevant signs of the unit, it will not be put back into the whole and participate in the next extraction.

Isometric sampling: it is to arrange all the units in the population into a graph or list according to a certain sign or order (commonly known as queuing), and then extract the sample units at equal distances or intervals.

Non-probabilistic 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.