Sampling box, also known as "sampling box" and "sampling structure", refers to the list or sorting number of 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.
Discrimination of the concepts of sampling frame and sampling unit
Sampling frame and sampling unit are a pair of basic categories of sampling. The mapping group of the actual population whose units meet the condition of "there is a definite correspondence with each unit of the actual population, and one or more specific units in the actual population can be found by virtue of this correspondence" is called sampling box, and the units that constitute the mapping group are called sampling units.
In other words, the population including all sampling units is called sampling box, and the units that make up the sampling box are called sampling units.
In fact, in order to facilitate the implementation of sampling, it is necessary to have a directory table, and each directory item in this directory table has a definite correspondence with each unit of the actual population, that is, according to a directory item, one or some specific units in the actual population can always be found. The sampling box is such a directory list.
Sampling boxes may appear in various forms: lists, manuals, maps, data packets? . Because no matter what form the sampling box takes, after sampling, the investigator must be able to find the specific sampling unit according to the sampling box.
Therefore, the sampling boxes must be orderly, that is, the sampling units must be numbered and arranged in a certain order; The sampling units contained in the sampling box must be "neither heavy nor leaking", otherwise sampling errors will occur.
The sampling unit not only refers to the catalog items that constitute the sampling framework, but also represents the actual overall specific units corresponding to the catalog items. Figuratively speaking, it is not only a shadow, but also an entity reflected by the shadow.
Although the sample literature is silent about this, it is helpful for readers to remember this. In order to distinguish these two different meanings of sampling unit, entity sampling unit is also called sample unit or sample point.
The sampling unit is not necessarily the smallest unit-the basic unit. A sampling unit can contain one or several basic units. In the simplest case, it contains only one basic unit.
In simple random sampling, the sampling unit is the basic unit; In cluster sampling, the cluster is the sampling unit, and the cluster may contain quite a few basic units. For example, in the mobile phone survey, we selected a residential building, which is a sampling unit, and every household in the building is a basic unit.