Among the most commonly used sampling methods, the most basic method is

Four basic sampling methods:

1. Simple random sampling: Simple random sampling refers to extracting a part of observation units in the population in a completely random way (that is, the probability that each observation unit is selected into the sample is the same). The common method is to number all the observation units in the population first, and then draw some observation units from them to form samples by lottery, random number table or computer-generated random number.

2. Systematic sampling: systematic sampling is also called equidistant sampling or mechanical sampling, that is, all individuals in the group are sorted and numbered according to the characteristics unrelated to the research phenomenon; Then, according to the sample content, the sampling interval k is specified; Randomly select I (i(i