Isometric random sampling is to arrange all units in the population in a certain symbolic order, then divide the number of units in the population by the number of units in the sample to get the sampling interval, and randomly select a unit as the sample unit in the first sampling interval; Finally, equidistant sampling is carried out according to the calculated sampling distance until N units are drawn.
Automatically shake (or generate) 10 natural numbers from 0 to 9 one by one with a special code shaker (or computer) according to the requirements of coding digits (such as a group of two digits, a group of three digits, a group of five digits or even a group of ten digits), and compile a certain number of numbers into tables for future reference. Any number in this list is equally likely to appear.
Direct sampling method is a common method, which is effective for both continuous and discrete random variables. For continuous random variables, the inverse function of distribution function must be obtained by applying this method. In addition, for discrete distribution, the advantage of direct sampling method is simple and easy to realize, but the disadvantage is that when there are many discrete points, the sampling speed is slow.
The lottery method is a method of numbering each unit of the survey population first, and then randomly drawing numbers until enough samples are drawn. It is suitable for transactions with relatively small overall capacity. Because it is simple and easy to realize, it is widely used.