There are various sampling methods, which can be divided into three categories:
A. Random sampling method, the starting point of sampling is purely to reduce the workload, and there is no certain pattern to follow. Since sampling is a blind selection of samples, the sampling results lack scientificity and reliability, so this method is generally not used.
B. Judgment sampling method, that is, a sampling method that determines the number of samples and evaluates the sampling results based on the subjective judgment of the auditors. Whether the samples drawn using this method can reflect the problems in the population depends on the experience and judgment ability of the customs auditors and their familiarity with the overall situation of the items being inspected. This method of using subjective judgment to determine the sampling has the advantages of highlighting the key points, being highly targeted, and being simple and easy to implement, but judgment sampling cannot guarantee that all units in the population have an equal chance of being selected into the sample, and there is no objective method to measure the reliability of the sample review results.
C. Statistical sampling method, that is, a sampling method in which customs auditors use the basic principles of statistical sampling to randomly select samples from the population and judge and infer the characteristics of the population based on the characteristics of the samples. This type of method has two significant characteristics: first, through precise statistical calculations, sampling risks can be controlled and measured; second, when customs inspectors infer the overall characteristics based on samples, they either rely on quantity estimation or on the frequency of occurrence of certain characteristics, that is, variables and attributes. Statistical sampling methods include specific techniques such as attribute sampling and variable sampling. Attribute sampling is a statistical sampling method that infers the overall characteristics based on the frequency of occurrence of a certain characteristic of the sample (such as correct or incorrect).