First, each unit of the survey population is numbered, and then the numbers are randomly selected until enough samples are extracted. Here, choose a case to illustrate that if you want to select three people from 10 as representatives, first number the 10 people in the whole crowd, write the numbers on the digital labels, put the digital labels in a container, stir them evenly, extract one digital label at a time and extract them three times in a row to get a sample with a capacity of 3. This is the lottery method, similar to the direct sampling method.
Simple random sampling takes every eligible individual as the sampling object, and makes every individual's chances of being selected into the sample equal through randomization. Because the randomization process can ensure that each individual has the same probability of being selected as the research sample, it can ensure the representativeness of the research sample to the whole population.
Extended data:
Advantages and disadvantages of simple random sampling
The advantage is simple, but the disadvantage is that when the overall capacity is large, it is time-consuming and inconvenient. Only applicable to the 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 unknown and difficult to classify, or the overall unit characteristics are different.
Three methods of simple random sampling
1, direct selection method
In other words, the sample is randomly selected directly 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.
Step 2 draw lots
First, all individuals in the population are numbered, and the numbers are written on numbered labels with the same shape and size, which can be balls, cards, paper strips, etc. Then put these digital labels in the same box and mix them evenly. Every time 1 number is extracted from it, a sample with capacity of is obtained continuously. When numbering individuals, you can also use existing numbers.
3. Random number table method
That is, the random number table is used as a sampling tool. Random number table (see example), also known as random number table, randomly arranges 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.
Baidu Encyclopedia-Simple Random Sampling