Random sampling: one by one from the crowd.
Systematic sampling: divide the population into several parts on average and extract from each part according to predetermined rules.
Stratified sampling: the population is divided into several layers with obvious differences and extracted by layers according to the proportion of the number of individuals in each layer.
2, the scope of use is different
Random sampling: the number of individuals in the group is small.
Systematic sampling: there are many individuals in the group.
Stratified sampling: the whole is composed of several parts with obvious differences.
Classification of random sampling methods
There are two kinds of random sampling:
First, simple random sampling
Pour 20 boxes of parts together, mix them evenly, number them one by one from 1 to 1000, and then take out 100 parts with irregular numbers from them by looking up the random number table or drawing lots. This is simple random sampling.
Second, systematic random sampling.
Pour 20 boxes of parts together, mix them evenly, number the parts from 1 to 1000 one by one, and then number them by looking up the random number table or drawing lots, such as 16, then the part numbers of the selected samples are 26, 36, 46, 56..., 906, 926 ...