Читать книгу Statistics and Probability with Applications for Engineers and Scientists Using MINITAB, R and JMP - Bhisham C. Gupta, Irwin Guttman - Страница 37

The population from which a sample is being selected is called a sampled population.

The population from which a sample is being selected is called a sampled population, and the population being studied is called the target population. Usually, these two populations coincide, since every effort should be made to ensure that the sampled population is the same as the target population. However, whether for financial reasons, a time constraint, a part of the population not being easily accessible, the unexpected loss of a part of the population, and so forth, we may have situations where the sampled population is not equivalent to the whole target population. In such cases, conclusions made about the sampled population are not usually applicable to the target population.

In almost all statistical studies, the conclusions about a population are based on the information drawn from a sample. In order to obtain useful information about a population by studying a sample, it is important that the sample be a representative sample; that is, the sample should possess the characteristics of the population under investigation. For example, if we are interested in studying the family incomes in the United States, then our sample must consist of representative families that are very poor, poor, middle class, rich, and very rich. One way to achieve this goal is by taking a random sample.