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.
draw lots
First, 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. Numbers can consist of balls, cards, paper strips, etc. Then put these numbers in the same box and mix them evenly. When drawing lots, draw 1 number each time, and draw several times in succession to get a sample with a capacity of. For example, when sampling the whole class, you can use the student's student number, seat number and so on. The lottery method is simple and easy, and it is suitable for the situation with a small total number of individuals.
Random number table method
Random number table method is to use random number table as a tool to sample. 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. It is characterized by no regularity in horizontal, vertical or interlaced reading. Therefore, sampling with this table can ensure the realization of the random principle and simplify the sampling work. The steps are as follows: ① Determine the overall scope. ② Determine the sample size; (3) Sampling the sample unit, that is, starting from any number in the random number table, reading it in a certain order (up, down, left and right) or at intervals, selecting numbers within the numbering range, not selecting numbers outside the range, and not selecting repeated numbers until the predetermined sample size is reached; ④ Arrange the selected numbers and list the names of the corresponding companies. Such as how to sample with a random number table. In order to check the quality of a product, we decided to select 10 from 40 products for inspection. When using the random number table to select this sample, you can follow the following steps: Step 1, first number 40 products, which can be numbered 00,01,02,,. Starting from any number in the random number table in appendix 1, for example, starting from the number 59 in the fifth column of row 8. For the convenience of explanation, we extract the line 6 to 1 0 in the appendix1as follows:16 22 77 94 39 49 54 54 8217 37 93 23 78 87 35 20 96 43 84 26 34 9164. +0 57 24 55 06 88 77 04 74 47 67 2 1 76 33 50 25 83 92 12 06 76 63 0 1 63 78 59 16 95 55 67 19 98 1 0 50 7 1 75 6 5438+02 86 73 58 07 44 39 52 38 79 33 2 1 12 34 29 78 64 56 07 82 52 42 07 44 38 15 5 1 00 / Kloc-0/3 42 99 66 02 79 57 60 86 32 44 09 47 27 96 54 4917 46 09 62 90 52 84 77 27 08 02 73 43 28 Step 3, read the selected number 59 to the right and get a two-digit number 59. Because 59 > 39, remove it; Continue reading to the right to get 16, and take it out; If we continue, we get 19, 10, 12, 07, 39, 38, 33, 2 1, and the last two digits are 12. Now that the front has been taken out, let's remove it and continue to take 34. The number of samples to be sampled is161912 07 39 38 33 2134 Note: when numbering n individuals in the population, you can start from 0, for example, when n = 100. In this way, all individuals in the population can be represented by two digits, which is convenient to use the random number table. When randomly selecting the number to start reading, the reading direction can be right, left, up, down, etc. In the process of reading every two digits above, a series of two digits are obtained. After removing unsatisfactory and repeated numbers, the numbers that appear in turn can be regarded as the number of individuals extracted from the population in turn. Because which number appears in each position in the random number table is equal probability, which two-digit number is read every time, that is, which individual's number is equal probability from the crowd. So the random number table is used to extract samples, which ensures that the probability of each individual being extracted is equal.