If there is no sampling box, it is impossible to calculate the probability of the sample unit, so it is impossible to carry out probability sampling.
Three forms of sampling frame.
1, specific sampling structure
That is, the sampling units can be listed in the form of a list. Comprise a directory structure, a region structure and a directory region composite structure. In this example, the roster of 20,000 students belongs to the directory structure. In the process of cluster sampling, we take the urban residents arranged according to the position of customary section as the candidate population, which is the regional structure. If some residents are selected instead of a comprehensive investigation, a roster of residents is needed, which becomes a composite structure.
2. Abstract sampling structure
In other words, there is no list of sampling units, only an open form. As long as it meets the survey conditions, it is an element in the sampling structure. For example, when a large retail mall conducts random interviews with buyers or consumers, its sampling structure is abstract and implicit.
3. Phased sampling structure
When profile design is adopted, different sampling structures can be made according to different sampling stages.