Random Sample

A census, which is a survey of every unit in a population, is rarely used to gather information in the social sciences because it is often costly, time consuming, or impracticable. Instead, researchers gather the information from a sample that is assumed to be representative of the population. Such a sample can be obtained by using a simple random sampling procedure . The resulting sample is called a simple random sample . The procedure selects a sample of size n with replacement from a finite population of size N > n such that each of the N n possible samples is equally likely to be selected. The probability of selecting a particular sample is 1/ N n . A sample unit is returned to the population once it has been selected so that the selection of a unit does not affect the selection of other units. In the social sciences, sampling is usually performed without replacement. The procedure selects a sample of size n from a finite population of size N > n such that each of the N !/[ n !( N – n )!] possible samples is equally likely to be selected. If the population is large, this procedure is adequate for all practical purposes.