Simple random sampling is the basis of other sampling methods, because it is the easiest to deal with in theory, and it is not difficult to realize when the total number of units n is not too large. But in practice, if n is quite large, simple random sampling is not good. First, it needs a sampling box containing all N cells; Secondly, the sample units obtained in this sampling are scattered, and the investigation is not easy to implement. Therefore, there are not many people who directly adopt simple random sampling in practice.
Characteristics of simple random sampling
The characteristics of simple random sampling are: the probability of each sample unit being extracted is equal, and each unit of the sample is completely independent, and there is no certain correlation and exclusion between them.
Sampling method of simple random sampling
The most basic sampling method of simple random sampling. Divided into repeated sampling and non-repeated sampling. In repeated sampling, the units extracted each time still return to the population, and the units in the sample may be extracted several times. In non-repeated sampling, the extracted units will not be put back into the population, and the units in the sample can only be extracted once. Non-repeated sampling was used in social survey.
The specific methods of simple random sampling are:
(1) draw lots. Sign all the units in the whole population one by one, stir them evenly and extract them.
② Random number table method. Number all the cells in the population, and then extract them from any starting point (any row or column) in the random number table from left to right or from right to left, up or down until the required sample size is reached.
Simple random sampling must have a complete sampling box, that is, a list of whole units. When the group is too large, the workload of making such a sampling box is huge, and there are many situations, which makes it impossible to obtain the group list. Therefore, pure random sampling is rarely used in large-scale social surveys.