Brief introduction of simple random sampling:
Generally speaking, assuming that a population contains n individuals, if a sample is extracted from it one by one, and the probability of each individual being extracted is equal, then such a sampling method is called simple random sampling.
Features:
(1) Simple random sampling requires that the total number of samples n to be sampled is limited.
(2) The number n of simple random samples is less than or equal to the number n of the sample population.
(3) Extract simple random samples from the population one by one.
(4) Simple random sampling is a kind of sampling that cannot be put back.
(5) The probability of each individual being systematically sampled is n/n. ..
Main disadvantages:
It is only applicable to a limited number of overall units, otherwise the numbering work is heavy; For complex people, the representativeness of the sample is difficult to guarantee; You can't use the known information of the whole. This method is effective when the market survey scope is limited, or the survey object is unclear and difficult to classify, or the characteristics of the whole unit are different.
Sampling method:
1, direct selection method.
Direct sampling method, that is, direct random sampling from the population. For example, a number of goods are randomly selected from the shelves for inspection; Choose several stalls from the farmer's market stalls for investigation or visit.
2. Draw lots.
Firstly, all individuals in the population are numbered (the numbering range can be 1 to n), and the numbers are written on numbers with the same shape and size, which can be balls, cards, paper strips, etc. Then put these numbers in the same box and mix them evenly.
When drawing lots, every time 1 number is drawn, a sample with a capacity of is obtained. When numbering individuals, you can also use the existing number, for example, when taking samples from the whole class, you can use the student's student number and seat number. The lottery method is simple and easy, and it is suitable for the situation that there are not many individuals in the whole population.
3. Random number table method.
Random number table method, that is, using random number table as a tool for sampling. Random number table, also known as random number table, is to randomly arrange 10 numbers from 0 to 9 into a table for future reference. Its characteristic is that no matter horizontal reading, vertical reading or interlaced reading is irregular. Therefore, using this table for sampling can ensure the realization of the random principle and simplify the sampling work.