Sampling frame, also known as "sampling frame" and "sampling structure", refers to the roster or sorting number that lists the overall units that can be selected as samples to determine the overall sampling range and structure. After designing the sampling frame, you can choose the required number of units by drawing lots or according to the random number table. 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, sampling units can be listed as 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: that is, 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. Staged sampling structure: When adopting staged sampling design, different sampling structures can be generated according to different sampling stages.