Different Samples from the Same Population
The discussion in Chapter 7 dealt with the fact that sometimes random samples represent the populations from which they are drawn very accurately and sometimes they don’t. Random selection is no guarantee of representativeness. Random sample selection does, however, make it possible to apply some very powerful tools for assessing how likely it is that a sample is unrepresentative to a particular degree. This is because, with the unbiased samples that random selection produces, we can say something about how often particular degrees of unrepresentativeness occur, on average.