Classified sampling is a mathematical method, which aims to simplify the steps and minimize the time consumption.
- Chinese name
- Classified sampling
- Type
- Mathematical method
Simple random sampling , also called Pure random sampling 。 It means that the survey units are randomly selected from the population without any grouping, classification, queuing, etc. The characteristics are: the probability of each sample unit being selected is equal, each sample unit is completely independent, and there is no certain correlation and exclusion between them. Simple random sampling is the basis of other sampling forms. This method is usually used only when there is a small degree and number of differences between the overall units. It is applicable to situations with large overall quantity and large degree of difference. First, the overall units shall be classified and stratified according to their degree of difference or a certain feature, and then the sample units shall be randomly selected from each category or layer. stratified sampling In fact, it is the combination of scientific grouping, or classification and random principle. Stratified sampling can be divided into equal sampling and unequal sampling. When the difference between the total number and various types is too large, unequal sampling can be used. It is organized in the same way as simple random sampling and equidistant sampling, except for stratification or classification. 
