Random sampling means that every individual in the group has an equal chance to be selected. If the researcher takes samples from the phone book in a random way (such as using a random number table), it can be guaranteed that the numbers taken are random samples of all the numbers listed in the phone book.

The law of probability ensures that within a certain error range, a large enough and true random sample can always represent the whole population, which will include women, ethnic minorities, married people and the elderly with roughly the same proportion as the whole population. The "cultural perspective" in this chapter describes the existing cultural and social diversity of the American population.

Sample introduction:

Specimen is a part of the individual observed or investigated, and the whole is the whole research object. The total number of elements extracted from the tested population and the number of individuals in the sample are called sample size. Generally speaking, the content of the sample is related to the unit. For example, the eyesight survey of 300 middle school students in a middle school, the sample is the eyesight of 300 middle school students, and the sample size is 300.

The process of selecting samples is called sampling, and the sampling methods are different according to different objects.