1, simple random sampling: the operation is simple and the selection deviation can be reduced. Disadvantages: We may not choose many individual elements that we are really interested in.
2. Systematic sampling: the first individual is randomly selected, and other individuals are selected at a fixed "sampling interval". That is to say, assuming that the overall size is x and the sample size is n, the next individual to be selected will be separated from the previous individual by x/n intervals. Advantages: simple operation. Disadvantages: If there are potential patterns when we choose items in the crowd, it may also lead to deviations.
3. Stratified sampling: According to different characteristics, divide the whole into different groups and select samples from these subgroups. For example, according to gender and category, people are divided into subgroups (called layers), and an equal number of people are selected from these subgroups to form samples. Scope of application: it is necessary to represent all subgroups of the whole, provided that the characteristics of the whole can be identified and distinguished.
4. Whole sampling: Divide the whole into different subgroups (groups) and randomly select a complete group as a sample. Scope of application: data is concentrated in a specific area or a specific field.
random sampling
Random sampling requires strict compliance with the principle of probability, and each sampling unit has the same probability of being drawn and can be reproduced. Random sampling is often used when the population is small, and its main feature is to extract from the population one by one. Random sampling can be divided into simple random sampling, systematic sampling, stratified sampling and cluster sampling.
1, draw lots. Generally speaking, the lottery method is to number N individuals in the group, write the numbers on the digital labels, put the digital labels into a container, and after stirring evenly, extract one digital label from it every time and extract it for N times continuously to get a sample with a capacity of N. The lottery method is simple and easy, and is suitable for the minority in the group.
2. Random number method. In random sampling, another commonly used method is random number method, that is, random number table, random number dice or computer-generated random number are used for sampling.